# CVE-2026-31966: htslib: HTSlib is a library for reading and writing bioinformatics file formats

CVE-2026-31966 is fixed in htslib on 1 platform by DEBIAN-CVE-2026-31966 (version 1.24-2), released March 18, 2026. It is not reported as exploited. Patch Radar priority: Urgent.

- Web page: https://patchblox.com/security/cve/CVE-2026-31966
- Priority: Urgent
- CVSS: 9.1 (critical)
- EPSS: 0.0055
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Mar 18, 2026

## Description

HTSlib is a library for reading and writing bioinformatics file formats. CRAM is a compressed format which stores DNA sequence alignment data. As one method of removing redundant data, CRAM uses reference-based compression so that instead of storing the full sequence for each alignment record it stores a location in an external reference sequence along with a list of differences to the reference at that location as a sequence of "features". When decoding CRAM records, the reference data is stored in a char array, and parts matching the alignment record sequence are copied over as necessary. Due to insufficient validation of the feature data series, it was possible to make the `cram_decode_seq()` function copy data from either before the start, or after the end of the stored reference either into the buffer used to store the output sequence for the cram record, or into the buffer used to build the SAM `MD` tag.  This allowed arbitrary data to be leaked to the calling function. This bug may allow information about program state to be leaked.  It may also cause a program crash through an attempt to access invalid memory. Versions 1.23.1, 1.22.2 and 1.21.1 include fixes for this issue. There is no workaround for this issue.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | htslib Debian 14 | 1.24-2 | [DEBIAN-CVE-2026-31966](https://patchblox.com/security/data/fix/linux/debian-cve-2026-31966.md) | Mar 18, 2026 |

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Data as of 2026-11-09T01:18:40Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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