Buffer overflow in Klauspost Compress
CVE-2026-63209
compress provides various compression algorithms. Prior to version 1.18.7, a signed integer overflow vulnerability in s2.NewDict() allows an attacker to bypass repeat index validation by supplying a dictionary with a uvarint-encoded repeat value exceeding MaxInt64. When Dict.Encode() is subsequently called, the overflowed negative repeat value causes an out-of-bounds memory access via unsafe.Pointer arithmetic, crashing the process with SIGSEGV. This issue has been patched in version 1.18.7.
Vulnerability class: Integer Overflow
Published · last modified .
CVSS v3 metric
CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.
EPSS exploit prediction
No EPSS score from FIRST.org yet. New CVEs usually get one within a few days; no score means no signal yet, not low risk. How EPSS works.
Affected products
- Klauspost Compress — versions < 1.18.7
Weakness classification (CWE)
References
Frequently asked questions
- What is CVE-2026-63209?
- CVE-2026-63209 is a high-severity vulnerability in Klauspost Compress, classified under Integer Overflow or Wraparound. CVSS score: 7.5/10. Published 2026-09-29.
- How severe is CVE-2026-63209?
- High severity. CVSS v3 base score is 7.5 out of 10.