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CVE-2026-63209— Integer Overflow or Wraparound and Out-of-bounds Write in compress

Quick assessment

Affected
klauspost compress
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

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 MaxI

CVSS 7.5 · High
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I. Basic Information for CVE-2026-63209

Vulnerability Information

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Vulnerability Title
Integer Overflow or Wraparound and Out-of-bounds Write in compress
Source: CVE Program / CVE List V5
Vulnerability Description
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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
整数溢出或超界折返
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
klauspost compress < 1.18.7 -

II. Public POCs for CVE-2026-63209

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III. Intelligence Information for CVE-2026-63209

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Other References for CVE-2026-63209 (3)

IV. Related Vulnerabilities

Same weakness: CWE-190

V. Comments for CVE-2026-63209

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