CVE-2026-43860Network attack vector

Authentication failure via truncated CRAM-MD5 digest

Published May 4, 2026 · Updated May 4, 2026

Off-by-one error in Mutt before 2.3.2 causes IMAP CRAM-MD5 authentication to fail when a long password's digest contains a zero byte. The hmac_md5 function in imap/auth_cram.c copies the 16-byte raw MD5 result with string-oriented strfcpy, which stops at a zero byte and always reserves space for a terminator. The path requires a password longer than 64 bytes; Debian characterizes the outcome as failed authentication in a corner case with no security impact.

CVSS severity3.7
Low
EPSS probability0.16%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Off-by-one error in Mutt before 2.3.2 causes IMAP CRAM-MD5 authentication to fail when a long password's digest contains a zero byte. The hmac_md5 function in imap/auth_cram.c copies the 16-byte raw MD5 result with string-oriented strfcpy, which stops at a zero byte and always reserves space for a terminator. The path requires a password longer than 64 bytes; Debian characterizes the outcome as failed authentication in a corner case with no security impact.

The record

CVE
CVE-2026-43860
Published
May 4, 2026
Updated
May 4, 2026
Vendor
Mutt
Product
Mutt
Classifications
CWE-193
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 4, 2026CVE publishedPublication date reported by the CVE source.
  2. May 4, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=0 <2.3.2

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Mutt · Muttversion=0 <2.3.2

Published CVSS scores

3.7MITRECVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-193Off-by-one Error

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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