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VulnerabilityPublished Updated

CVE-2026-42504: Go standard library mime · Inefficient Algorithmic Complexity

Affects Go standard library mimeSource CVE Database V5

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Not known to be exploited · CVSS 7.5 High : upgrade to 1.26.4 or 1.25.11 soon.

Data as of 30 Oct 2026, 12:04 UTC

CVSS 3.1 base score
7.5High
How severe the flaw is on the 0–10 CVSS scale.

Thin evidence

One scorer or none
CVSS scores by source
CISA-ADPCVSS 3.17.5
EPSS
0.5% chance of exploitation in 30 days – higher than 46% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
CISA SSVC
Exploitation
No evidence of active exploitation and no public proof of concept
Automatable
Attackers can reliably automate steps 1–4 of the kill chain
Technical impact
Limited control over the software or limited information exposure

CISA SSVC assessment, 2026-06-03.

Patch
Available – fixed in 1.26.4, 1.25.11
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 2 Jun 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponized: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 30 Oct 2026.

What to do

Upgrade Go standard library mime to 1.26.4 or 1.25.11.

Affected software

ProductAffectedFixed in
Go standard librarymimeAffected
  • >=1.26.0-0 <1.26.4
Fixed in
  • 1.26.4
Go standard librarymimeAffected
  • <1.25.11
Fixed in
  • 1.25.11
Gomimepkg:golang/mimeOther threatsAffected
  • <1.25.11
  • >=1.26.0-0 <1.26.4
Fixed in
  • 1.25.11
  • 1.26.4

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

Users should upgrade to Go standard library versions 1.25.11 or 1.26.4 or later, where this vulnerability has been fixed. No other mitigation is required as the issue is resolved in these official releases.

Description

Decoding a maliciously-crafted MIME header containing many invalid encoded-words can consume excessive CPU.

References

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