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CVE-2026-31963

HIGH CVSS 4.0: 8.8 EPSS 0.05%
Updated Mar 19, 2026
Samtools
Parameter Value
CVSS 8.8 (HIGH)
Affected Versions 1.22 — 1.22.2
Fixed In 1.21.1
Type CWE-129 (Improper Validation of Array Index), CWE-787 (Out-of-bounds Write), CWE-122 (Heap-based Buffer Overflow)
Vendor Samtools
Public PoC No

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 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.

Attack Parameters

Attack Vector
Network
Can be exploited remotely
Attack Complexity
Low
Easy to exploit
Attack Requirements
None
No additional conditions
Privileges Required
None
No privileges needed
User Interaction
None
No user interaction needed

Impact Assessment

Confidentiality
None
No data leak
Integrity
High
Complete data modification
Availability
Low
Partial disruption

CVSS Vector v4.0

Vulnerable Products 3

Configuration From (including) Up to (excluding)
Htslib Htslib
cpe:2.3:a:htslib:htslib:*:*:*:*:*:*:*:*
1.21.1
Htslib Htslib
cpe:2.3:a:htslib:htslib:*:*:*:*:*:*:*:*
1.22 1.22.2
Htslib Htslib
cpe:2.3:a:htslib:htslib:1.23:*:*:*:*:*:*:*