Raw vector
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/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:XSummary
CVE-2026-31963 is a high-severity Heap-based Buffer Overflow (CWE-122) vulnerability in Htslib Htslib. Its CVSS base score is 8.8 (High).
Operationally, exploitation aligns with the MITRE ATT&CK technique Exploitation for Privilege Escalation (T1068); ranked at the 28th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified map to SA-11 (Developer Testing and Evaluation) and SI-10 (Information Input Validation) — see the control section below for these in your framework.
Deeper analysis AI-assisted summary
Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.
CVE-2026-31963 is a heap buffer overflow vulnerability in HTSlib, a C library for reading and writing bioinformatics file formats such as CRAM, which stores compressed DNA sequence alignment data using reference-based compression. The issue stems from an out-by-one error in a test for CRAM features that extend beyond the record sequence extent, resulting in an invalid write of one attacker-controlled byte past the end of a heap buffer during feature decoding. This affects HTSlib versions prior to the patches in 1.23.1, 1.22.2, and 1.21.1, and is classified under CWE-122 (Heap-based Buffer Overflow), CWE-129 (Improper Validation of Array Index), and CWE-787 (Out-of-bounds Write), with a CVSS v3.1 base score of 8.1.
An attacker can exploit this vulnerability by crafting a malicious CRAM file and tricking a user into opening it with software linked to a vulnerable HTSlib version, such as bioinformatics tools like samtools. The attack is network-vector (AV:N) with low complexity (AC:L), requires no privileges (PR:N) but user interaction (UI:R), and has no scope change (S:U). Successful exploitation causes a heap buffer overflow, potentially leading to program crashes, unexpected overwriting of heap data and structures, or arbitrary code execution.
The HTSlib GitHub security advisory (GHSA-qgqh-h2q9-7w3c) and commit 8bcc9907be0f945ddc31796d64f078fa05456acd detail the fix, backported to maintenance branches for versions 1.23.1, 1.22.2, and 1.21.1. There is no workaround available, so users should update to a patched version immediately.
OWASP Top 10 for Web (2025)
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-12930
Vulnerability Data
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…
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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 these features, an out-by-one error in a test for CRAM features that appear beyond the extent of the CRAM record sequence could result in an invalid write of one attacker-controlled byte beyond the end of a 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. There is no workaround for this issue.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise Techniques
CVEs Like This One
Affected Assets
Mitigating Controls
Control response
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V1.4.1
Mitigating Controls (NIST 800-53 r5) AI
Developer testing and evaluation (including fuzzing and memory-error detectors) can discover heap overflows after they have been coded.
Input validation enforces bounds checking on data written to heap buffers, directly stopping the overflow condition from being introduced.
Requiring documented secure-development standards and tools can mandate bounds-checked coding practices that avoid the weakness.
Security engineering principles require use of memory-safe constructs and bounds-checked allocation routines that avoid introducing heap overflows.
Memory-protection mechanisms limit the ability of a heap overflow to execute attacker-controlled code or corrupt adjacent structures.
Mitigating Controls (NIST CSF 2.0) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.
Secure-development practices directly require bounds checking and safe memory handling that prevent heap overflows.
Vulnerability scanning and recording can discover heap-overflow flaws but does not prevent their introduction in code.
Timely patching removes known heap-overflow instances after they exist.
Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.
Security testing in development and acceptance can detect heap overflows before release.
Secure development lifecycle mandates practices that reduce the likelihood of introducing heap overflows.
Application security requirements can specify bounds-checking and safe memory APIs that mitigate heap overflows.
Secure architecture and engineering principles include memory-safety and input-validation controls that address heap overflows.
Secure coding standards directly prescribe techniques (safe functions, bounds checks) that prevent heap-based buffer overflows.
Change management can enforce review gates that catch unsafe memory operations before deployment.