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VulnerabilityPublished Updated

CVE-2026-39820: Go standard library net/mail · Inefficient Algorithmic Complexity

Affects Go standard library net/mailSource CVE Database V5

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Not known to be exploited · CVSS 7.5 High : upgrade to 1.26.3 or 1.25.10 soon.

Data as of 30 Oct 2026, 11:52 UTC

CVSS 3.1 base score
7.5High
How severe the flaw is on the 0–10 CVSS scale.
EPSS
0.7% chance of exploitation in 30 days – higher than 55% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch
Available – fixed in 1.26.3, 1.25.10
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 7 May 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 net/mail to 1.26.3 or 1.25.10.

Affected software

ProductAffectedFixed in
Go standard librarynet/mailAffected
  • >=1.26.0-0 <1.26.3
Fixed in
  • 1.26.3
Go standard librarynet/mailAffected
  • <1.25.10
Fixed in
  • 1.25.10
Gonet/mailpkg:golang/net/mailOther threatsAffected
  • =0
  • =1.26.0-0
Fixed in–
Gonet/mailpkg:golang/net/mailOther threatsAffected
  • <1.25.10
  • >=1.26.0-0 <1.26.3
Fixed in
  • 1.25.10
  • 1.26.3

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

AI-suggested

In the meantime, mitigating exposure by limiting or validating untrusted inputs to the affected functions may reduce risk, although no specific mitigation is officially recommended.

Description

Well-crafted inputs reaching ParseAddress, ParseAddressList, and ParseDate were able to trigger excessive CPU exhaustion and memory allocations.

References

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