# CVE-2026-39979: jqlang jq out-of-bounds read in jv_parse_sized

Source: https://junglewise.ai/threats/cve-2026-39979-jqlang-jq-out-of-bounds-read-in-jv-parse-sized  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-04-13. Updated: 2026-06-30  
License: CC BY 4.0 with a link back

CVE-2026-39979 · Severity: medium · CVSS 6.5 · Published 2026-04-13

jq is a widely used tool and library for processing JSON data. A security flaw was found in how the library handles malformed data when reporting errors. If an application uses this library to process untrusted data, an attacker could potentially crash the application or view small amounts of sensitive information from the computer's memory.

Technologies: [Jqlang Jq](https://junglewise.ai/threats/technologies/jq). Vendors: [Jqlang](https://junglewise.ai/threats/vendors/jqlang).

## Quick answers

**Is CVE-2026-39979 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-39979 being exploited in the wild.

**How severe is CVE-2026-39979?** Medium severity, with a CVSS score of 6.5, published 13 April 2026.

**Which products and versions are affected?** Jqlang Jq <= 1.8.1.

**Is there a fix for CVE-2026-39979?** A patch was published on 2026-04-13: Fix committed to jqlang/jq repository Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-39979 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-39979?** Check whether you run Jqlang Jq at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

An out-of-bounds read vulnerability exists in libjq's jv_parse_sized() API. While the API accepts a counted buffer with an explicit length, the error-handling path in jv_parse_sized_custom_flags() uses jv_string_fmt() with a %s format specifier to process the input buffer. This causes the underlying vsnprintf() to read past the intended buffer length until a NUL terminator is encountered. An attacker providing malformed JSON in a non-NUL-terminated buffer can trigger this OOB read, potentially resulting in information disclosure or a denial-of-service (crash). The issue is fixed in commit 2f09060afab23fe9390cce7cb860b10416e1bf5f and jq version 1.8.2.

## Affected products

- jqlang jq <= 1.8.1
- Red Hat Red Hat Enterprise Linux 8 1.6-12.el8_10

## Timeline

- 2026-04-13: advisory: GitHub Security Advisory GHSA-2hhh-px8h-355p published
- 2026-04-13: patched: Fix committed to jqlang/jq repository
- 2026-05-12: patched: Red Hat released security updates for RHEL 8

## References

- [https://github.com/jqlang/jq/commit/2f09060afab23fe9390cce7cb860b10416e1bf5f](https://github.com/jqlang/jq/commit/2f09060afab23fe9390cce7cb860b10416e1bf5f)
- [https://github.com/jqlang/jq/security/advisories/GHSA-2hhh-px8h-355p](https://github.com/jqlang/jq/security/advisories/GHSA-2hhh-px8h-355p)
- [https://access.redhat.com/errata/RHSA-2026:16252](https://access.redhat.com/errata/RHSA-2026:16252)
- [https://access.redhat.com/errata/RHSA-2026:16692](https://access.redhat.com/errata/RHSA-2026:16692)
- [https://access.redhat.com/errata/RHSA-2026:16693](https://access.redhat.com/errata/RHSA-2026:16693)
- [https://access.redhat.com/errata/RHSA-2026:18040](https://access.redhat.com/errata/RHSA-2026:18040)
- [https://access.redhat.com/errata/RHSA-2026:18042](https://access.redhat.com/errata/RHSA-2026:18042)

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