CVE-2026-43861Network attack vector

URL truncation via decoded NUL byte

Published May 4, 2026 · Updated May 4, 2026

Null-byte injection in Mutt before 2.3.2 allows remote attackers to alter URL interpretation through a percent-encoded NUL. The url_pct_decode function accepts %00 and writes the decoded zero byte into the URL buffer, causing later C-string processing to stop at that byte. Exploitation requires a crafted URL that reaches this decoder; published sources establish limited integrity impact but do not identify the downstream operation altered.

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

Null-byte injection in Mutt before 2.3.2 allows remote attackers to alter URL interpretation through a percent-encoded NUL. The url_pct_decode function accepts %00 and writes the decoded zero byte into the URL buffer, causing later C-string processing to stop at that byte. Exploitation requires a crafted URL that reaches this decoder; published sources establish limited integrity impact but do not identify the downstream operation altered.

The record

CVE
CVE-2026-43861
Published
May 4, 2026
Updated
May 4, 2026
Vendor
Mutt
Product
Mutt
Classifications
CWE-158
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

5.3SUSECVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
6.9SUSECVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N
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

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-158Improper Neutralization of Null Byte or NUL Character

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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