CVE-2026-39979: jq: Out-of-Bounds Read in jv_parse_sized() Error Formatting for Non-NUL-Terminated Counted Buffers

Vulnerability summary

CVE-2026-39979 is a high (CVSS 8.2) Out-of-bounds Read vulnerability in jqlang jq. EPSS estimates a 0.56% chance of exploitation in the next 30 days, higher than 46.6% of scored vulnerabilities. 1 public exploit is recorded.

Timeline

1. 13-04-2026
   PublishedVulnerability first disclosed.
2. 15-07-2026
   Last modifiedVulnerability information updated.

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.

• CWE-125Out-of-bounds ReadThe product reads data past the end, or before the beginning, of the intended buffer.