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No exploitation reportedFix available

CVE-2026-31970

No exploitation reported by the sources we read.

  • Published2026-03-18
  • Fixed in1.22.2 · 1.21
  • WeaknessCWE-122 · CWE-1284 · CWE-131

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

Description

HTSlib is a library for reading and writing bioinformatics file formats. GZI files are used to index block-compressed GZIP [BGZF] files. In the GZI loading function, `bgzf_index_load_hfile()`, it was possible to trigger an integer overflow, leading to an under- or zero-sized buffer being allocated to store the index. Sixteen zero bytes would then be written to this buffer, and, depending on the result of the overflow the rest of the file may also be loaded into the buffer as well. If the function did attempt to load the data, it would eventually fail due to not reading the expected number of records, and then try to free the overflowed heap buffer. Exploiting this bug causes a heap buffer overflow. If a user opens a file crafted to exploit this issue, it could lead to the program crashing, or overwriting of data and heap structures in ways not expected by the program. It may be possible to use this to obtain arbitrary code execution. Versions 1.23.1, 1.22.2 and 1.21.1 include fixes for this issue. The easiest work-around is to discard any `.gzi` index files from untrusted sources, and use the `bgzip -r` option to recreate them.

Timeline

dates in UTC
  1. 2026-03-1820:16CVE publishedNVD

Versions per branch

NVD
Htslib
BranchAffectedFixed in
1.22≥ 1.22, < 1.22.21.22.2
1.21< 1.211.21
1.23= 1.23no fix published

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Products declared by the CNA1 product

As GitHub_M, the CNA that assigned this CVE, declared them in the CVE record; versions as written.

  • samtools htslib
    Affected
    • = < 1.21.1no fix stated
    • = >= 1.22, < 1.22.2no fix stated
    • = = 1.23no fix stated

Source: the CNA record (CVE Program), © The MITRE Corporation,CVE Terms of UseCVE recordupdated 2026-03-18

Distribution builds and vendor advisories

Packages from OSV.dev and products from the vendors' CSAF advisories.

version not verifiedVersions not verified: read as OSV.dev and the vendors publish them, not checked against each vendor's release list.

Packages

  • htslibUbuntu:Pro:18.04:LTSall versions · no fixed version listed
  • htslibUbuntu:Pro:16.04:LTSall versions · no fixed version listed
  • htslibUbuntu:Pro:14.04:LTSall versions · no fixed version listed
  • htslibUbuntu:26.10all versions · no fixed version listed
  • htslibUbuntu:26.04:LTSall versions · no fixed version listed
  • htslibUbuntu:25.10all versions · no fixed version listed
  • htslibUbuntu:24.04:LTSall versions · no fixed version listed
  • htslibUbuntu:22.04:LTSall versions · no fixed version listed

4 more package ranges on OSV.dev

Full record on NVD

Fix

  1. Update Htslib to 1.22.2 · 1.21

Advisories and patches

Detection

Nuclei template
none so far
ProjectDiscovery
Exploit-DB
no entry
Exploit-DB
Proof of concept
Metasploit modules
none listed
Metasploit Framework

Sources

  • CISA-ADPSSVC decisionnone2026-03-18
  • CNACVSS 4.07.1known since 2026-10-23
  • NVDCVSS 3.18.1read 2026-10-23
  • CNAweakness (CWE)CWE-122, CWE-1284, CWE-131, CWE-190, CWE-787known since 2026-10-23
  • FIRST EPSSEPSS score0.5 %2026-11-09
  • OSVaffected packages—

Identifiers

Technical details

CVSS v3 Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:H
CVSS 4.0 vector
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:H/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:X/V:X/RE:X/U:X
Published
2026-03-18
Last Modified
2026-06-17
NVD status
Analyzed

Frequently asked questions

What is CVE-2026-31970?

HTSlib is a library for reading and writing bioinformatics file formats. GZI files are used to index block-compressed GZIP [BGZF] files. In the GZI loading function, `bgzf_index_load_hfile()`, it was possible to trigger an integer overflow, leading to an under- or zero-sized buffer being allocated to store the index. Sixteen zero bytes would then be written to this buffer, and, depending on the result of the overflow the rest of the file may also be loaded into the buffer as well. If the function did attempt to load the data, it would eventually fail due to not reading the expected number of records, and then try to free the overflowed heap buffer. Exploiting this bug causes a heap buffer overflow. If a user opens a file crafted to exploit this issue, it could lead to the program crashing, or overwriting of data and heap structures in ways not expected by the program. It may be possible to use this to obtain arbitrary code execution. Versions 1.23.1, 1.22.2 and 1.21.1 include fixes for this issue. The easiest work-around is to discard any `.gzi` index files from untrusted sources, and use the `bgzip -r` option to recreate them.

Is CVE-2026-31970 actively exploited?

Active exploitation of CVE-2026-31970 has not been confirmed. Its EPSS score was 0.5% on 2026-11-09, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2026-31970?

CVE-2026-31970 has a CVSS v3 base score of 8.1 (HIGH severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:H.

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