CVE-2025-61962Network attack vector

Service crash via malformed SMTP AUTH reply

Published Oct 4, 2025 · Updated Oct 4, 2025

Improper input validation in fetchmail before 6.5.6 allows remote attackers to crash its SMTP client via a malformed 334 AUTH reply. The SMTP_auth routine in smtp.c searches the response for a required space, then increments the null result and passes address 0x1 to the SASL challenge decoder. Exploitation requires configured esmtpname and esmtppassword values with plugout and mda inactive; a crash also terminates daemon mode.

CVSS severity5.9
Medium
EPSS probability0.41%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper input validation in fetchmail before 6.5.6 allows remote attackers to crash its SMTP client via a malformed 334 AUTH reply. The SMTP_auth routine in smtp.c searches the response for a required space, then increments the null result and passes address 0x1 to the SASL challenge decoder. Exploitation requires configured esmtpname and esmtppassword values with plugout and mda inactive; a crash also terminates daemon mode.

The record

CVE
CVE-2025-61962
Published
Oct 4, 2025
Updated
Oct 4, 2025
Vendor
fetchmail
Product
fetchmail
Classifications
CWE-142, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Oct 4, 2025CVE publishedPublication date reported by the CVE source.
  2. Oct 4, 2025Record 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=5.9.9 <6.5.6

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

fetchmail · fetchmailversion=5.9.9 <6.5.6

Published CVSS scores

5.9SUSECVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
5.9MITRECVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

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-142Improper Neutralization of Value Delimiters
T1499.004Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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