CVE-2026-63435Network attack vector

Address spoofing via greedy encoded-word decoding

Published Sep 1, 2026 · Updated Sep 2, 2026

Interpretation conflict in Mikel Lindsaar Mail before 2.9.1 allows remote attackers to spoof sender or recipient addresses. Mail::Utilities.q_value_decode and Mail::Utilities.b_value_decode use a single match with a greedy charset capture, decoding only the first RFC 2047 encoded-word and mishandling adjacent text. Applications that display or authorize against decoded From, To, or Reply-To values can accept a different address than raw-header validation indicates, enabling phishing or authorization bypass.

CVSS severity5.3
Medium
EPSS probability0.33%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Interpretation conflict in Mikel Lindsaar Mail before 2.9.1 allows remote attackers to spoof sender or recipient addresses. Mail::Utilities.q_value_decode and Mail::Utilities.b_value_decode use a single match with a greedy charset capture, decoding only the first RFC 2047 encoded-word and mishandling adjacent text. Applications that display or authorize against decoded From, To, or Reply-To values can accept a different address than raw-header validation indicates, enabling phishing or authorization bypass.

The record

CVE
CVE-2026-63435
Published
Sep 1, 2026
Updated
Sep 2, 2026
Vendor
Mikel Lindsaar
Product
Mail
Classifications
CWE-436, T1566
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Sep 1, 2026CVE publishedPublication date reported by the CVE source.
  2. Sep 2, 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=< 2.9.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Mikel Lindsaar · Mailversion=< 2.9.1

Published CVSS scores

5.3GitHub CNACVSS:3.1/AV:N/AC:L/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-436Interpretation Conflict
T1566Phishing

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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