Raw 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:XSummary
CVE-2026-31969 is a high-severity Heap-based Buffer Overflow (CWE-122) vulnerability in Htslib Htslib. Its CVSS base score is 7.1 (High).
Operationally, exploitation aligns with the MITRE ATT&CK technique Exploitation for Privilege Escalation (T1068); ranked at the 26th 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-2026-31969 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. The issue stems from an out-by-one error in the `cram_byte_array_stop_decode_char()` function during decoding of data encoded with the `BYTE_ARRAY_STOP` method. This flaw allows a single attacker-controlled byte to be written beyond the end of a heap allocation when checking for a full output buffer, affecting HTSlib versions prior to the patched releases.
A remote attacker can exploit this vulnerability by crafting a malicious CRAM file and tricking a user into opening it with an application linked to a vulnerable version of HTSlib. No privileges are required (PR:N), and the attack is feasible over a network (AV:N) with low complexity (AC:L), though it relies on user interaction (UI:R). Successful exploitation triggers a heap buffer overflow, potentially causing the program to crash, overwriting adjacent heap data or structures, and enabling arbitrary code execution in some cases. The CVSS v3.1 base score of 8.1 reflects high impacts on integrity (I:H) and availability (A:H) with no confidentiality impact (C:N), linked to CWEs-122 (Heap-based Buffer Overflow) and CWE-787 (Out-of-bounds Write).
The HTSlib security advisory (GHSA-q4cj-f4h5-fqgc) and associated patch commit (88cdf69e4b83bb550ab4f6f7134892c2ad1978f4) confirm fixes in versions 1.23.1, 1.22.2, and 1.21.1. There is no workaround available, so security practitioners should ensure dependent applications upgrade to these or later versions and validate inputs when processing untrusted CRAM files.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-12944
Vulnerability Data
HTSlib is a library for reading and writing bioinformatics file formats. CRAM is a compressed format which stores DNA sequence alignment data using a variety of encodings and compression methods. When reading data encoded using the `BYTE_ARRAY_STOP` method, an out-by-one…
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error in the `cram_byte_array_stop_decode_char()` function check for a full output buffer could result in a single attacker-controlled byte being written beyond the end of a heap allocation. 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.