spectre-meltdown-checker/DEVELOPMENT.md

Project Overview

spectre-meltdown-checker is a single self-contained shell script (spectre-meltdown-checker.sh) that detects system vulnerability to several transient execution CPU CVEs (Spectre, Meltdown, and related). It supports Linux and BSD (FreeBSD, NetBSD, DragonFlyBSD) on x86, amd64, ARM, and ARM64.

The script must stay POSIX-compatible, and not use features only available in specific shells such as bash or zsh. The local keyword is accepted however.

Project Mission

This tool exists to give system administrators simple, actionable answers to two questions:

1. Am I vulnerable?
2. What do I have to do to mitigate these vulnerabilities on my system?

The script does not run exploits and cannot guarantee security. It reports whether a system is affected, vulnerable, or mitigated against known transient execution vulnerabilities, and provides detailed insight into the prerequisites for full mitigation (microcode, kernel, hypervisor, etc.).

Why this tool still matters

Even though the Linux sysfs hierarchy (/sys/devices/system/cpu/vulnerabilities/) now reports mitigation status for most vulnerabilities, this script provides value beyond what sysfs offers:

• Independent of kernel knowledge: A given kernel only understands vulnerabilities known at compile time. This script's detection logic is maintained independently, so it can identify gaps a kernel doesn't yet know about.
• Detailed prerequisite breakdown: Mitigating a vulnerability can involve multiple layers (microcode, host kernel, hypervisor, guest kernel, software). The script shows exactly which pieces are in place and which are missing.
• Offline kernel analysis: The script can inspect a kernel image before it is booted (--kernel, --config, --map), verifying it carries the expected mitigations.
• Backport-aware: It detects actual capabilities rather than checking version strings, so it works correctly with vendor kernels that silently backport or forward-port patches.
• Covers gaps in sysfs: Some vulnerabilities (e.g. Zenbleed) are not reported through sysfs at all.

Terminology

These terms have precise meanings throughout the codebase and output:

• Affected: The CPU hardware, as shipped from the factory, is known to be concerned by a vulnerability. Says nothing about whether the vulnerability is currently exploitable.
• Vulnerable: The system uses an affected CPU and has no (or insufficient) mitigations in place, meaning the vulnerability can be exploited.
• Mitigated: A previously vulnerable system has all required layers updated so the vulnerability cannot be exploited.

Branch Model

The project uses 4 branches organized in two pipelines (production and dev/test). Developers work on the source branches; CI builds the monolithic script and pushes it to the corresponding output branch.

Branch	Contents	Pushed by
test	Dev/test source (split files + Makefile)	Developers
test-build	Monolithic test script (built artifact)	CI from test
source	Production source (split files + Makefile)	Developers
source-build	Monolithic test script (built artifact)	CI from source
master	Monolithic production script (built artifact)	PR by developers from source-build

• source and test contain the split source files and the Makefile. These are the branches developers commit to.
• master, source-build and test-build contain only the monolithic spectre-meltdown-checker.sh built by CI. Nobody commits to these directly.
• master is the preexisting production branch that users pull from. It cannot be renamed.
• test-build is a testing branch that users can pull from to test pre-release versions.
• source-build is a preprod branch to prepare the artifact before merging to master.

Typical workflow:

1. Feature/fix branches are created from test and merged back into test.
2. CI builds the script and pushes it to test-build for testing.
3. When ready for release, test is merged into source.
4. CI builds the script and pushes it to source-build for production.
5. Developer creates a PR from source-build to master.

Versioning

The project follows semantic versioning in the format X.Y.Z:

• X = the current year, in YY format.
• Y = the number of CVEs supported by the script, which corresponds to the number of files under src/vulns/.
• Z = MMDDVAL, where MMDD is the UTC build date and VAL is a 3-digit value (000–999) that increases monotonically throughout the day, computed as seconds_since_midnight_UTC * 1000 / 86400.

The version is patched automatically by build.sh into the VERSION= variable of the assembled script. The source file (src/libs/001_core_header.sh) carries a placeholder value that is overwritten at build time.

Linting and Testing

# Assemble the final script
make build

# Lint the generated script
make fmt-check shellcheck

# Run the script (requires root for full results)
sudo ./spectre-meltdown-checker.sh

# Run specific tests that we might have just added (variant name)
sudo ./spectre-meltdown-checker.sh --variant l1tf --variant taa

# Run specific tests that we might have just added (CVE name)
sudo ./spectre-meltdown-checker.sh --cve CVE-2018-3640 --cve CVE-2022-40982

# Batch JSON mode (CI validates exactly 19 CVEs in output)
sudo ./spectre-meltdown-checker.sh --batch json | jq '.[] | .CVE' | wc -l  # must be 19

# Update microcode firmware database
sudo ./spectre-meltdown-checker.sh --update-fwdb

# Docker
docker-compose build && docker-compose run --rm spectre-meltdown-checker

There is no separate test suite. CI (.github/workflows/check.yml) runs shellcheck, tab-indentation checks, a live execution test validating 19 CVEs, Docker builds, and a firmware DB update test that checks for temp file leaks.

Architecture

The entire tool is a single bash script with no external script dependencies. Key structural sections:

• Output/logging functions (~line 253): pr_warn, pr_info, pr_verbose, pr_debug, explain, pstatus, pvulnstatus — verbosity-aware output with color support
• CPU detection (~line 2171): parse_cpu_details, is_intel/is_amd/is_hygon, read_cpuid, read_msr, is_cpu_smt_enabled — hardware identification via CPUID/MSR registers
• Microcode database (embedded): Intel/AMD microcode version lookup via read_mcedb/read_inteldb; updated automatically via .github/workflows/autoupdate.yml
• Kernel analysis (~line 1568): extract_kernel, try_decompress — extracts and inspects kernel images (handles gzip, bzip2, xz, lz4, zstd compression)
• Vulnerability checks: 19 check_CVE_<year>_<number>() functions, each with _linux() and _bsd() variants. Uses whitelist logic (assumes affected unless proven otherwise)
• Main flow (~line 6668): Parse options → detect CPU → loop through requested CVEs → output results (text/json/nrpe/prometheus) → cleanup

Key Design Principles

These rules are non-negotiable and govern how every part of the script is written:

1. Production-safe

It must always be okay to run this script in a production environment.

• 1a. Non-destructive: Never modify the system. If the script loads a kernel module it needs (e.g. cpuid, msr), it must unload it on exit.
• 1b. Report only: Never attempt to "fix" or "mitigate" any vulnerability, or modify any configuration. The script reports status and leaves all decisions to the sysadmin.
• 1c. No exploit execution: Never run any kind of exploit or proof-of-concept. This would violate rule 1a, could cause unpredictable system behavior, and may produce wrong conclusions (especially for Spectre-class PoCs that require very specific build options and prerequisites).

2. Never hardcode kernel versions

Never look at the kernel version string to determine whether it supports a mitigation. This would defeat the script's purpose: it must detect mitigations in unknown, vendor-patched, or backported kernels. Similarly, do not blindly trust what sysfs reports when it is possible to verify directly.

3. Never hardcode microcode versions

Never look at the microcode version to determine whether it has the proper mitigation mechanisms. Instead, probe for the mechanisms themselves (CPUID bits, MSR values), as the kernel would.

4. Assume affected unless proven otherwise (whitelist approach)

When a CPU is not explicitly known to be unaffected by a vulnerability, assume that it is affected. This conservative default has been the right call since the early Spectre/Meltdown days and remains sound.

5. Offline mode

The script can analyze a non-running kernel via --kernel, --config, --map flags, allowing verification before deployment.

CVE Inclusion Criteria

A vulnerability should be supported by this tool when mitigating it requires kernel modifications, microcode modifications, or both.

A vulnerability is out of scope when:

• Mitigation is handled entirely by a driver or userspace software update (e.g. CVE-2019-14615, which requires an Intel driver update).
• The vulnerability is a regression from a bad backport and cannot be detected without hardcoding kernel versions (violates rule 2).
• The vendor has determined it is not a new attack and issued no kernel or microcode changes, leaving nothing for the script to check.
• The industry has collectively decided not to address the vulnerability (no mitigations exist), leaving nothing to verify.

When evaluating whether to add a new CVE, check the information-tagged issues for prior discussion and precedent.

POSIX Compliance

The script must run on both Linux and BSD systems (FreeBSD, NetBSD, DragonFlyBSD). This means all external tool invocations must use only POSIX-specified options. Many tools have GNU extensions that are not available on BSD, or BSD extensions that are not available on GNU/Linux. When in doubt, test on both.

Common traps to avoid:

Tool	Non-portable usage	Portable alternative
sed	-r (GNU extended regex flag)	-E (accepted by both GNU and BSD)
grep	-P (Perl regex, GNU only)	Use awk or rework the pattern
sort	-V (version sort, GNU only)	Extract numeric fields and compare with awk or shell arithmetic
cut	-w (whitespace delimiter, BSD only)	awk '{print $N}'
stat	-c %Y (GNU format)	Try GNU first, fall back to BSD: stat -c %Y ... 2>/dev/null || stat -f %m ...
date	-d @timestamp (GNU only)	Try GNU first, fall back to BSD: date -d @ts ... 2>/dev/null || date -r ts ...
xargs	-r (no-op if empty, GNU only)	Guard with a prior [ -n "..." ] check, or accept the harmless empty invocation
readlink	-f (canonicalize, GNU only)	Use only in Linux-specific code paths, or reimplement with cd/pwd
dd	iflag=, oflag= (GNU only)	Use only in Linux-specific code paths (e.g. /dev/cpu/*/msr)

When a tool genuinely has no portable equivalent, restrict the non-portable call to a platform-specific code path (i.e. inside a BSD-only or Linux-only branch) and document why.

Return Codes

0 = not vulnerable, 2 = vulnerable, 3 = unknown, 255 = error

Variable naming conventions

This script uses the following naming rules for variables:

UPPER_SNAKE_CASE : Constants and enums (e.g. READ_MSR_RET_OK, EAX), declared with readonly on the assignment line (e.g. readonly FOO="bar"). When they're used as values affected to "Out-parameters" of a function, they should follow the <FUNC>_RET_* pattern. Such variables should be declared right above the definition of the function they're dedicated to. Other general constants go at the top of the file, below the VERSION affectation. opt_* : Command-line options set during argument parsing (e.g. opt_verbose, opt_batch). cpu_* : CPU identification/state filled by parse_cpu_details() (e.g. cpu_family, cpu_model). cap_* : CPU capability flags read from hardware/firmware (e.g. cap_verw_clear, cap_rdcl_no). All cap_* variables are set in check_cpu(). They come in two flavors: - Immunity bits (cap_*_no): The CPU vendor declares this hardware is not affected by a vulnerability. The _no suffix mirrors the vendor's own bit naming (e.g. RDCL_NO, GDS_NO, TSA_SQ_NO). These are consumed in is_cpu_affected() to mark a CPU as immune. - Mitigation bits (all other cap_*): Microcode or hardware provides a mechanism to work around a vulnerability the CPU does have (e.g. cap_verw_clear, cap_ibrs, cap_ssbd). These are consumed in check_CVE_*_linux() functions to assess mitigation status. affected_* : Per-CVE vulnerability status from is_cpu_affected() (e.g. affected_l1tf). ret_<func>_* : "Out-parameters" set by a function for its caller (e.g. ret_read_cpuid_value, ret_read_msr_msg). The matches the function name so ownership is obvious, these variables can't be written to by any other function than , nor by toplevel. g_* : Other global (i.e. non-local) variables that don't match cases previously described. <name> : Scratch/temporary variables inside functions (e.g. core, msg, col). These must be declared as local. These must not match any naming pattern above. Any variable that is only used in the scope of a given function falls in this category.

Additionally, all vars must start with a [a-z] character, never by an underscore.

Function naming conventions

Functions follow two naming tiers:

public_function : Top-level functions called directly from the main flow or from other public functions. Examples: parse_cpu_details, read_cpuid, check_CVE_2017_5754.

_private_function : Utility/helper functions that exist solely to factorize code shared by other functions. These must never be called directly from the top-level main flow. Examples: _echo, _emit_json, _cve_registry_field.

How to Implement a New CVE Check

Adding a new CVE follows a fixed pattern. Every check uses the same three-function structure and the same decision algorithm. This section walks through both.

Prerequisites

Before writing code, verify the CVE meets the inclusion criteria (see "CVE Inclusion Criteria" above). The vulnerability must require kernel and/or microcode changes to mitigate.

Step 1: Create the Vulnerability File

Create src/vulns/CVE-YYYY-NNNNN.sh. The file must contain exactly three functions:

# vim: set ts=4 sw=4 sts=4 et:
####################
# SHORT_NAME section

# CVE-YYYY-NNNNN SHORT_NAME (one-line description) - entry point
check_CVE_YYYY_NNNNN() {
	check_cve 'CVE-YYYY-NNNNN'
}

# CVE-YYYY-NNNNN SHORT_NAME (one-line description) - Linux mitigation check
check_CVE_YYYY_NNNNN_linux() {
	# ... (see Step 3)
}

# CVE-YYYY-NNNNN SHORT_NAME (one-line description) - BSD mitigation check
check_CVE_YYYY_NNNNN_bsd() {
	if ! is_cpu_affected "$cve"; then
		pvulnstatus "$cve" OK "your CPU vendor reported your CPU model as not affected"
	else
		pvulnstatus "$cve" UNK "your CPU is affected, but mitigation detection has not yet been implemented for BSD in this script"
	fi
}

The entry point calls check_cve, which prints the CVE header and dispatches to _linux() or _bsd() based on $g_os. If BSD mitigations are not yet understood, use the stub above — it correctly reports UNK rather than a false OK.

Step 2: Register the CVE in the CPU Affection Logic

In src/libs/200_cpu_affected.sh, add an affected_yourname variable and populate it inside is_cpu_affected(). The variable follows the whitelist principle: assume affected (1) unless you can prove the CPU is immune (0). Two kinds of evidence can prove immunity:

• Static identifiers: CPU vendor, family, model, stepping — these identify the hardware design.
• Hardware immunity cap_* bits: CPUID or MSR bits that the CPU vendor defines to explicitly declare "this hardware is not affected" (e.g. cap_rdcl_no for Meltdown, cap_ssb_no for Variant 4, cap_gds_no for Downfall, cap_tsa_sq_no/cap_tsa_l1_no for TSA). These are read in check_cpu() and stored as cap_* globals.

Never use microcode version strings.

Important: Do not confuse hardware immunity bits with mitigation capability bits. A hardware immunity bit (e.g. GDS_NO, TSA_SQ_NO) declares that the CPU design is architecturally free of the vulnerability — it belongs here in is_cpu_affected(). A mitigation capability bit (e.g. VERW_CLEAR, MD_CLEAR) indicates that updated microcode provides a mechanism to work around a vulnerability the CPU does have — it belongs in the check_CVE_YYYY_NNNNN_linux() function (Phase 2), where it is used to determine whether mitigations are in place.

Step 3: Implement the Linux Check

The _linux() function follows a standard algorithm with four phases:

Phase 1 — Initialize and check sysfs:

check_CVE_YYYY_NNNNN_linux() {
	local status sys_interface_available msg
	status=UNK
	sys_interface_available=0
	msg=''
	if sys_interface_check "$VULN_SYSFS_BASE/vuln_name"; then
		sys_interface_available=1
		status=$ret_sys_interface_check_status
	fi

sys_interface_check reads /sys/devices/system/cpu/vulnerabilities/<name> and parses the kernel's own assessment into ret_sys_interface_check_status (OK/VULN/UNK) and ret_sys_interface_check_fullmsg. If the sysfs file doesn't exist (older kernel, or the CVE predates kernel awareness), it returns false and sys_interface_available stays 0.

Phase 2 — Custom detection (kernel + runtime):

Guarded by if [ "$opt_sysfs_only" != 1 ]; then so users who trust sysfs can skip it.

This is where the real detection lives. Check for mitigations at each layer:

• Kernel support: Determine whether the kernel carries the mitigation code. Three sources of evidence are available, and any one of them is sufficient:

  • Kernel image ($g_kernel): Search for strings or symbols that prove the mitigation code is compiled in.

    if grep -q 'mitigation_string' "$g_kernel"; then
        kernel_mitigated="found mitigation evidence in kernel image"
    fi
    

    Guard with if [ -n "$g_kernel_err" ]; then first — the kernel image may be unavailable.

  • Kernel config ($g_kernel_config): Look for the CONFIG_* option that enables the mitigation.

    if [ -n "$g_kernel_config" ] && grep -q '^CONFIG_MITIGATION_NAME=y' "$g_kernel_config"; then
        kernel_mitigated="found mitigation config option enabled"
    fi
    

  • System.map ($g_kernel_map): Look for function names directly linked to the mitigation.

    if [ -n "$g_kernel_map" ] && grep -q 'mitigation_function_name' "$g_kernel_map"; then
        kernel_mitigated="found mitigation function in System.map"
    fi
    

  Each source may independently be unavailable (offline mode without the file, or stripped kernel), so check all that are present. A match in any one confirms kernel support.

• Runtime state (live mode only): Read MSRs, check cpuinfo flags, parse dmesg, inspect debugfs.

  if [ "$opt_live" = 1 ]; then
      read_msr 0xADDRESS
      ret=$?
      if [ "$ret" = "$READ_MSR_RET_OK" ]; then
          # check specific bits in ret_read_msr_value_lo / ret_read_msr_value_hi
      fi
  else
      pstatus blue N/A "not testable in offline mode"
  fi
  

• Microcode capabilities: Check CPUID bits or MSR flags that indicate the CPU firmware supports the mitigation. Never compare microcode version numbers directly.

Close the opt_sysfs_only block with the forced-sysfs fallback:

	elif [ "$sys_interface_available" = 0 ]; then
		msg="/sys vulnerability interface use forced, but it's not available!"
		status=UNK
	fi

Phase 3 — CPU affection gate:

	if ! is_cpu_affected "$cve"; then
		pvulnstatus "$cve" OK "your CPU vendor reported your CPU model as not affected"

If the CPU is not affected, nothing else matters — report OK and return. This overrides any sysfs or custom detection result.

Phase 4 — Final status determination:

For affected CPUs, combine the evidence from Phase 2 into a final verdict:

	elif [ "$opt_sysfs_only" != 1 ]; then
		if [ "$microcode_ok" = 1 ] && [ -n "$kernel_mitigated" ]; then
			pvulnstatus "$cve" OK "Both kernel and microcode mitigate the vulnerability"
		elif [ "$microcode_ok" = 1 ]; then
			pvulnstatus "$cve" OK "Microcode mitigates the vulnerability"
		elif [ -n "$kernel_mitigated" ]; then
			pvulnstatus "$cve" OK "Kernel mitigates the vulnerability"
		else
			pvulnstatus "$cve" VULN "Neither kernel nor microcode mitigate the vulnerability"
			explain "Remediation advice here..."
		fi
	else
		pvulnstatus "$cve" "$status" "$ret_sys_interface_check_fullmsg"
	fi
}

The exact combination logic depends on the CVE. Some require both microcode and kernel fixes (report VULN if either is missing). Others are mitigated by either layer alone (report OK if one is present). Some also require SMT to be disabled — check with is_cpu_smt_enabled().

Cross-Cutting Features

Several command-line options affect the logic inside _linux() checks. New CVE implementations must account for them where relevant.

--explain (opt_explain)

When the user passes --explain, the explain() function prints actionable "How to fix" remediation advice. Call explain whenever reporting a VULN status, so the user knows what concrete steps to take:

pvulnstatus "$cve" VULN "Neither kernel nor microcode mitigate the vulnerability"
explain "Update your kernel to a version that includes the mitigation, and update your CPU microcode. If you are using a distro, make sure you are up to date."

The text should be specific: mention kernel parameters to set (nosmt), sysctl knobs to toggle, or which component needs updating. If SMT must be disabled, say so explicitly. Multiple explain calls can be made for different failure paths, each tailored to the specific gap found. explain is a no-op when --explain was not passed, so it is always safe to call.

--paranoid (opt_paranoid)

Paranoid mode raises the bar for what counts as "mitigated". In normal mode, conditional mitigations or partial defenses may be accepted as sufficient. In paranoid mode, only the maximum security configuration qualifies as OK.

The most common effect is requiring SMT (Hyper-Threading) to be disabled. For example, MDS and TAA mitigations are considered incomplete in paranoid mode if SMT is still enabled, because a sibling thread could still exploit the vulnerability:

if [ "$opt_paranoid" != 1 ] || [ "$kernel_smt_allowed" = 0 ]; then
    pvulnstatus "$cve" OK "Microcode and kernel mitigate the vulnerability"
else
    pvulnstatus "$cve" VULN "Mitigation is active but SMT must be disabled for full protection"
fi

Other paranoid-mode effects include requiring unconditional (rather than conditional) L1D flushing, or requiring TSX to be fully disabled. When implementing a new CVE, consider whether there is a stricter configuration that paranoid mode should enforce and add the appropriate opt_paranoid branches.

--vmm (opt_vmm)

The --vmm option tells the script whether the system is a hypervisor host running untrusted virtual machines. It accepts three values: auto (default, auto-detect by looking for qemu/kvm/xen processes), yes (force hypervisor mode), or no (force non-hypervisor mode). The result is stored in g_has_vmm by the check_has_vmm() function.

Some vulnerabilities (e.g. L1TF/CVE-2018-3646, ITLBMH/CVE-2018-12207) only matter — or require additional mitigations — when the host is running a hypervisor with untrusted guests. If g_has_vmm is 0, the system can be reported as not vulnerable to these VMM-specific aspects:

if [ "$g_has_vmm" = 0 ]; then
    pvulnstatus "$cve" OK "this system is not running a hypervisor"
else
    # check hypervisor-specific mitigations (L1D flushing, EPT, etc.)
fi

CVEs that need VMM context should call check_has_vmm early in their _linux() function. Note the interaction with paranoid mode: when --paranoid is active and --vmm was not explicitly set, the script assumes a hypervisor is present (g_has_vmm=2), erring on the side of caution.

Step 4: Wire Up and Test

1. Add the CVE name mapping in the cve2name() function so the header prints a human-readable name.
2. Build the monolithic script with make.
3. Test live: Run the built script and confirm your CVE appears in the output and reports a sensible status.
4. Test batch JSON: Run with --batch json and verify the CVE count incremented by one (currently 19 → 20).
5. Test offline: Run with --kernel/--config/--map pointing to a kernel image and verify the offline code path reports correctly.
6. Lint: Run shellcheck on the monolithic script and fix any warnings.
7. Update dist/README.md: Add details about the new CVE check (name, description, what it detects) so that the user-facing documentation stays in sync with the implementation.

Key Rules to Remember

• Never hardcode kernel or microcode versions — detect capabilities directly (design principles 2 and 3).
• Assume affected by default — only mark a CPU as unaffected when there is positive evidence (design principle 4).
• Always handle both live and offline modes — use $opt_live to branch, and print N/A "not testable in offline mode" for runtime-only checks when offline.
• Use explain() when reporting VULN to give actionable remediation advice (see "Cross-Cutting Features" above).
• Handle --paranoid and --vmm when the CVE has stricter mitigation tiers or VMM-specific aspects (see "Cross-Cutting Features" above).
• All indentation must use tabs (CI enforces this).
• Stay POSIX-compatible — no bashisms, no GNU-only flags in portable code paths.

Function documentation headers

Every function must have a documentation header immediately above its definition. The format is:

# <short description of what the function does>
# Sets: <comma-separated list of global variables written by this function>
# Returns: <return value constants or description>
<function_name>()
{

Header lines (all optional except the description):

Line	When to include	Example
Description	Always	# Read CPUID register value across one or all cores
# Args:	When the function takes positional parameters	# Args: $1=msr_address $2=cpu_index(optional, default 0)
# Sets:	When the function writes any ret_* or other global variable	# Sets: ret_read_cpuid_value, ret_read_cpuid_msg
# Returns:	When the function uses explicit return codes (constants)	# Returns: READ_CPUID_RET_OK | READ_CPUID_RET_ERR | READ_CPUID_RET_KO
# Callers:	Required for _private (underscore-prefixed) functions	# Callers: pvulnstatus, pstatus

Rules:

• The # Sets: line is critical — it makes global side effects explicit so any reviewer can immediately see what a function mutates.
• The # Callers: line is required for all _-prefixed functions. It documents which functions depend on this helper, making it safe to refactor.
• Keep descriptions to one line when possible. If more context is needed, add continuation comment lines before the structured lines.
• Parameter documentation uses $1=name format. Append (optional, default X) for optional parameters.

Full example:

# Read a single MSR register on one CPU core
# Args: $1=msr_address $2=cpu_index(optional, default 0)
# Sets: ret_read_msr_value, ret_read_msr_msg
# Returns: READ_MSR_RET_OK | READ_MSR_RET_ERR | READ_MSR_RET_KO
read_msr()
{

Private function example:

# Emit a single CVE result as a JSON object to the batch output buffer
# Args: $1=cve_id $2=status $3=message
# Callers: _record_result
_emit_json()
{