# CVE-2026-43894: jqlang jq out-of-bounds write in decNumberFromString

Source: https://junglewise.ai/threats/cve-2026-43894-jqlang-jq-out-of-bounds-write-in-decnumberfromstring  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-05-11. Updated: 2026-05-11  
License: CC BY 4.0 with a link back

CVE-2026-43894 · Severity: medium · CVSS 6.2 · Published 2026-05-11

jq is a widely used command-line tool for processing and transforming JSON data. A vulnerability in how it handles extremely large numbers (over 2 billion digits) can cause the program to crash or behave unpredictably. This could be used by an attacker to disrupt automated workflows or services that process untrusted data using jq.

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

## Quick answers

**Is CVE-2026-43894 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-43894 being exploited in the wild.

**How severe is CVE-2026-43894?** Medium severity, with a CVSS score of 6.2, published 11 May 2026.

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

**Is there a fix for CVE-2026-43894?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-43894 attacked?** It is attacked with local access, in a software library.

**Am I affected by CVE-2026-43894?** 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

A signed integer overflow exists in the D2U() macro within the bundled decNumber library (vendor/decNumber/decNumber.c). When decNumberFromString is passed a number literal containing INT_MAX-1 digits, the macro's arithmetic overflows, resulting in a negative value. This negative value bypasses heap-allocation size checks, causing the function to use a small stack buffer while attempting to write approximately 1.4 GiB of attacker-controlled data to an offset far below the stack frame. While raw JSON parsing is protected by separate length limits, the vulnerability is reachable via the 'tonumber' function on strings generated within jq. This typically results in a denial of service (crash), though memory corruption is possible depending on the system's memory layout.

## Affected products

- jqlang jq <= 1.8.1

## Timeline

- 2026-05-06: advisory: GitHub Security Advisory published
- 2026-05-11: disclosed: CVE-2026-43894 published to NVD

## References

- [https://github.com/jqlang/jq/security/advisories/GHSA-5v7p-2r57-2g4g](https://github.com/jqlang/jq/security/advisories/GHSA-5v7p-2r57-2g4g)

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