CVE-2026-31963Network attack vector

Heap corruption via off-by-one CRAM feature validation

Published Mar 18, 2026 · Updated Mar 18, 2026

Heap buffer overflow in the HTSlib CRAM reader before 1.21.1, 1.22 through 1.22.1, and 1.23 allows attackers to corrupt memory. In cram_decode_seq, an off-by-one boundary test accepts sequence-writing features one position beyond a CRAM record, causing one attacker-controlled byte to be written past a heap buffer. Exploitation requires a user or process to open a crafted CRAM file and can crash the process or corrupt heap data and control structures.

CVSS severity8.8
High
EPSS probability0.35%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Heap buffer overflow in the HTSlib CRAM reader before 1.21.1, 1.22 through 1.22.1, and 1.23 allows attackers to corrupt memory. In cram_decode_seq, an off-by-one boundary test accepts sequence-writing features one position beyond a CRAM record, causing one attacker-controlled byte to be written past a heap buffer. Exploitation requires a user or process to open a crafted CRAM file and can crash the process or corrupt heap data and control structures.

The record

CVE
CVE-2026-31963
Published
Mar 18, 2026
Updated
Mar 18, 2026
Vendor
Samtools
Product
HTSlib
Classifications
CWE-787, CWE-122, CWE-129, T1203, T1204.002
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 18, 2026CVE publishedPublication date reported by the CVE source.
  2. Mar 18, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 1.21.1
  2. Affected versionversion=>= 1.22, < 1.22.2
  3. Affected versionversion== 1.23

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Samtools · HTSlibversion=< 1.21.1; version=>= 1.22, < 1.22.2; version== 1.23

Published CVSS scores

8.8GitHub, Inc.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
8.1NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-787Out-of-bounds Write
CWE-122Heap-based Buffer Overflow
CWE-129Improper Validation of Array Index
T1203Exploitation for Client Execution
T1204.002Malicious File

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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