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CVE-2026-31971

HTSlib CRAM decoder vulnerable to buffer overflow

7.1 HighFix available

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_LEN method, the cram_byte_array_len_decode() failed to validate that the amount of data being unpacked matched the size of the output buffer where it was to be stored. Depending on the data series being read, this could result either in a heap or a stack overflow with attacker-controlled bytes. Depending on the data stream this could result either in a heap buffer overflow or a stack overflow. If a user opens a file crafted to exploit this issue it could lead to the program crashing, overwriting of data structures on the heap or stack in ways not expected by the program, or changing the control flow of 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 profile

How easy it is to exploit

Attack vector
Network
Complexity
Low
Privileges needed
None
User interaction
Passive

What an attacker can affect

Confidentiality
None
Integrity
High
Availability
Low

Exploit likelihood

0.36%Up 0.2 points since Mar 19, 2026
90%50%10%1%

What each source reports

CVE List Score used 7.1

HTSlib CRAM decoder vulnerable to buffer overflow

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_LEN method, the cram_byte_array_len_decode() failed to validate that the amount of data being unpacked matched the size of the output buffer where it was to be stored. Depending on the data series being read, this could result either in a heap or a stack overflow with attacker-controlled bytes. Depending on the data stream this could result either in a heap buffer overflow or a stack overflow. If a user opens a file crafted to exploit this issue it could lead to the program crashing, overwriting of data structures on the heap or stack in ways not expected by the program, or changing the control flow of 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.

Record
CVE-2026-31971
CVSS 4.0
7.1 HighCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:H/VA:L/SC:N/SI:N/SA:N
Weakness
CWE-121, CWE-122, CWE-787, CWE-1284
Updated
2026-11-02
EUVDEUVD-2026-12948 7.1

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_LEN method, the cram_byte_array_len_decode() failed to validate that the amount of data being unpacked matched the size of the output buffer where it was to be stored. Depending on the data series being read, this could result either in a heap or a stack overflow with attacker-controlled bytes. Depending on the data stream this could result either in a heap buffer overflow or a stack overflow. If a user opens a file crafted to exploit this issue it could lead to the program crashing, overwriting of data structures on the heap or stack in ways not expected by the program, or changing the control flow of 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.

Record
EUVD-2026-12948
CVSS 4.0
7.1 HighCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:H/VA:L/SC:N/SI:N/SA:N
Updated
2026-11-02
NVD 7.1

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_LEN method, the cram_byte_array_len_decode() failed to validate that the amount of data being unpacked matched the size of the output buffer where it was to be stored. Depending on the data series being read, this could result either in a heap or a stack overflow with attacker-controlled bytes. Depending on the data stream this could result either in a heap buffer overflow or a stack overflow. If a user opens a file crafted to exploit this issue it could lead to the program crashing, overwriting of data structures on the heap or stack in ways not expected by the program, or changing the control flow of 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.

Record
CVE-2026-31971
CVSS 4.0
7.1 HighCVSS: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
CVSS 3.1
8.1 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:H
Weakness
CWE-121, CWE-122, CWE-787, CWE-1284
Updated
2026-11-02
OSV 7.1

HTSlib CRAM decoder vulnerable to buffer overflow

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_LEN method, the cram_byte_array_len_decode() failed to validate that the amount of data being unpacked matched the size of the output buffer where it was to be stored. Depending on the data series being read, this could result either in a heap or a stack overflow with attacker-controlled bytes. Depending on the data stream this could result either in a heap buffer overflow or a stack overflow. If a user opens a file crafted to exploit this issue it could lead to the program crashing, overwriting of data structures on the heap or stack in ways not expected by the program, or changing the control flow of 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.

Record
CVE-2026-31971
CVSS 4.0
7.1 HighCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:H/VA:L/SC:N/SI:N/SA:N
Weakness
CWE-121, CWE-122, CWE-1284, CWE-787
Updated
2026-11-02
OSVDEBIAN-CVE-2026-31971 8.1

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_LEN method, the cram_byte_array_len_decode() failed to validate that the amount of data being unpacked matched the size of the output buffer where it was to be stored. Depending on the data series being read, this could result either in a heap or a stack overflow with attacker-controlled bytes. Depending on the data stream this could result either in a heap buffer overflow or a stack overflow. If a user opens a file crafted to exploit this issue it could lead to the program crashing, overwriting of data structures on the heap or stack in ways not expected by the program, or changing the control flow of 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.

Record
DEBIAN-CVE-2026-31971
CVSS 3.1
8.1 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:H
Updated
2026-11-02
OSVUBUNTU-CVE-2026-31971 7.1

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_LEN method, the cram_byte_array_len_decode() failed to validate that the amount of data being unpacked matched the size of the output buffer where it was to be stored. Depending on the data series being read, this could result either in a heap or a stack overflow with attacker-controlled bytes. Depending on the data stream this could result either in a heap buffer overflow or a stack overflow. If a user opens a file crafted to exploit this issue it could lead to the program crashing, overwriting of data structures on the heap or stack in ways not expected by the program, or changing the control flow of 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.

Record
UBUNTU-CVE-2026-31971
CVSS 4.0
7.1 HighCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:H/VA:L/SC:N/SI:N/SA:N
CVSS 3.1
8.1 HighCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:H
Updated
2026-11-02

Affected products

Affected packages

Affected packages
PackageAffectedFixed
htslib
Debian:12
All versions, plus listed versions
1.16+ds-31.17+ds-0+exp11.17+ds-11.18+ds-0+exp11.18+ds-1
Show 15 moreShow less
1.19+ds-0+exp01.19+ds-11.19+ds-1+exp11.19+ds-1.11.20+ds-11.20+ds-21.21+ds-0+exp11.21+ds-0+exp21.21+ds-11.22.1+ds-11.22.1+ds-21.22.1+ds2-11.24-11.24-21.24-3
None known
htslib
Debian:13
All versions, plus listed versions
1.21+ds-11.22.1+ds-11.22.1+ds-21.22.1+ds2-11.24-11.24-21.24-3
None known
htslib
Debian:14
before 1.24-2, plus listed versions
1.21+ds-11.22.1+ds-11.22.1+ds-21.22.1+ds2-11.24-1
1.24-2
htslib
Ubuntu:Pro:14.04:LTS
All versions, plus listed versions
0.2.0~rc3-10.2.0~rc3-1ubuntu0.1~esm1
None known
htslib
Ubuntu:Pro:16.04:LTS
All versions, plus listed versions
1.2.1-11.2.1-21.2.1-2ubuntu11.2.1-2ubuntu1+esm1
None known
htslib
Ubuntu:Pro:18.04:LTS
All versions, plus listed versions
1.5-11.5-4ubuntu11.6-3ubuntu11.6-41.6-4build11.7-21.7-2ubuntu0.1~esm1
None known
htslib
Ubuntu:20.04:LTS
All versions, plus listed versions
1.9-101.9-111.9-121.10.2-2ubuntu11.10.2-2ubuntu21.10.2-31.10.2-3ubuntu0.1
None known
htslib
Ubuntu:22.04:LTS
All versions, plus listed versions
1.13+ds-21.13+ds-2build1
None known
htslib
Ubuntu:24.04:LTS
All versions, plus listed versions
1.17+ds-11.18+ds-11.19+ds-1.1build21.19+ds-1.1build3
None known
htslib
Ubuntu:25.10
All versions, plus listed versions
1.21+ds-1
None known
htslib
Ubuntu:26.10
All versions, plus listed versions
1.22.1+ds2-11.22.1+ds2-1build1
None known
htslib
Ubuntu:26.04:LTS
All versions, plus listed versions
1.21+ds-11.22.1+ds2-1
None known

History

History
RecordedChangedSources
first indexedCVE List, EUVD, NVD, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2026-31971 is a high vulnerability (CVSS 7.1) in Htslib, published March 18, 2026. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.36%, the 29th percentile. Fixed in htslib 1.24-2.

References

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