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.

• https://github.com/klauspost/compress/commit/539243b8823ee8f03e49969823d57c348c917536
• https://github.com/klauspost/compress/releases/tag/v1.18.7
• https://github.com/klauspost/compress/security/advisories/GHSA-259r-337f-4rfw
• https://github.com/klauspost/compress/security/advisories/GHSA-259r-337f-4rfw