← Vulnerability feed

Vulnerability record · CVE-2026-31966 · published 18 March 2026

CVE-2026-31966: Htslib out-of-bounds read vulnerability

HHtslib · Htslib

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.

6.9 CVSS 4.0 Medium EPSS 0.65% · top 50.7% CWE-125 · Out-of-bounds readCWE-129 · CWE-129
6.9CVSS 4.0 base score
0.65%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
4References
17 Jun 2026Last modified by NVD

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.

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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://github.com/samtools/htslib/commit/22ec5230ef95769ab009420da69568c7e530af28 Patch
https://github.com/samtools/htslib/commit/2a45eb129d703ad27f9fabc8169f0e94d3c69fa3 Patch
https://github.com/samtools/htslib/commit/4a5ef25eb1fb3d64438103316fffe423b2c3f5f4 Patch
https://github.com/samtools/htslib/security/advisories/GHSA-5cj8-mj52-8vp3 PatchVendor Advisory

Track CVE-2026-31966 inside VULONE

Watch it alongside the ransomware crews, C2 infrastructure and forum chatter that reference it, query it through the API and pull it into your SIEM over TAXII.

Start free Open in platform

Related vulnerabilities

Same products first, then exploited flaws of the same weakness class.

9.8CVE-2018-13845Htslib out-of-bounds read vulnerabilityAn issue has been found in HTSlib 1.8. It is a buffer over-read in sam_parse1 in sam.c.EPSS 1.6%9.8CVE-2017-1000206Htslib memory buffer overflow vulnerabilitysamtools htslib library version 1.4.0 and earlier is vulnerable to buffer overflow in the CRAM rANS codec resulting in potential arbitrary code execu…EPSS 2.0%8.8CVE-2026-31968Htslib stack-based buffer overflow vulnerabilityHTSlib is a library for reading and writing bioinformatics file formats. CRAM is a compressed format which stores DNA sequence alignment data using a…EPSS 0.52%8.8CVE-2026-31963Htslib heap-based buffer overflow vulnerabilityHTSlib is a library for reading and writing bioinformatics file formats. CRAM is a compressed format which stores DNA sequence alignment data. As one…EPSS 0.52%8.8CVE-2026-31962Htslib heap-based buffer overflow vulnerabilityHTSlib is a library for reading and writing bioinformatics file formats. CRAM is a compressed format which stores DNA sequence alignment data. While …EPSS 0.59%8.8CVE-2020-36403Htslib out-of-bounds write vulnerabilityHTSlib through 1.10.2 allows out-of-bounds write access in vcf_parse_format (called from vcf_parse and vcf_read).EPSS 1.6%7.5CVE-2018-13843Htslib vulnerabilityAn issue has been found in HTSlib 1.8. It is a memory leak in bgzf_getline in bgzf.c. NOTE: the software maintainer's position is that the "failure t…EPSS 1.5%7.5CVE-2018-13844Htslib memory leak vulnerabilityAn issue has been found in HTSlib 1.8. It is a memory leak in fai_read in faidx.c. NOTE: This has been disputed with the assertion that this vulnerab…EPSS 1.4%

Source: NIST National Vulnerability Database (record CVE-2026-31966), CISA KEV, FIRST EPSS (scores of 2026-09-29). This page is refreshed as NVD updates the record.