CVE-2026-31970
HTSlib BGZF index file reader has a heap buffer overflow
- Published
- Updated
- Reserved
- Assigned by
- GitHub_M
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.
Scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| GitHub_MCNA (assigner) | 4.0 | High7.1 | 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 |
| NVDNVD · Analyzed | 4.0 | High7.1 | 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 |
- EPSS (exploitation in 30 days)
- 0.48% · top 58% of all CVEs (6 Nov 2026)
- CISA SSVC
- Exploitation: none · Automatable: no · Technical impact: partial
The list uses the assigner's score when there is one, then CISA's, then NVD's: High 7.1.
Weakness
- CWE-122: Heap-based Buffer Overflow (opens in a new tab)All about CWE-122 and its CVEs
- CWE-131: Incorrect Calculation of Buffer Size (opens in a new tab)All about CWE-131 and its CVEs
- CWE-190: Integer Overflow or Wraparound (opens in a new tab)All about CWE-190 and its CVEs
- CWE-787: Out-of-bounds Write (opens in a new tab)All about CWE-787 and its CVEs
- CWE-1284: Improper Validation of Specified Quantity in Input (opens in a new tab)All about CWE-1284 and its CVEs
Affected products
References (3)
- https://github.com/samtools/htslib/security/advisories/GHSA-p345-84hx-fq6q (opens in a new tab)x_refsource_CONFIRM
- https://github.com/samtools/htslib/commit/6dd0d7d0e9e7e2e173a28969e624db8bc8bb5828 (opens in a new tab)x_refsource_MISC
- http://www.openwall.com/lists/oss-security/2026/03/18/9 (opens in a new tab)
Sources
The same CVE in the primary databases and aggregators, to check against.
- CVE.org record (opens in a new tab)
- CVE List JSON (GitHub) (opens in a new tab)
- NVD (opens in a new tab)
- FIRST EPSS (opens in a new tab)
- OSV.dev (opens in a new tab)
- GitHub Advisories (opens in a new tab)
- CIRCL Vulnerability-Lookup (opens in a new tab)
Badge for a README or a ticket
[](https://trackcve.app/cve/CVE-2026-31970)Record last updated .