CVE-2026-27651Network attack vector

Mail proxy worker crash via stale password length

Published Mar 24, 2026 · Updated Mar 24, 2026

NULL pointer dereference in F5 NGINX Open Source and NGINX Plus allows remote attackers to crash mail proxy worker processes. The auth_http request builder clears s->passwd.data but leaves its length nonzero, so a retry dereferences a null password pointer during CRAM-MD5 authentication. Exposure requires the mail auth_http module, CRAM-MD5 or APOP, and an authentication server response carrying Auth-Wait.

CVSS severity8.7
High
EPSS probability0.94%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

NULL pointer dereference in F5 NGINX Open Source and NGINX Plus allows remote attackers to crash mail proxy worker processes. The auth_http request builder clears s->passwd.data but leaves its length nonzero, so a retry dereferences a null password pointer during CRAM-MD5 authentication. Exposure requires the mail auth_http module, CRAM-MD5 or APOP, and an authentication server response carrying Auth-Wait.

The record

CVE
CVE-2026-27651
Published
Mar 24, 2026
Updated
Mar 24, 2026
Vendor
F5 Networks
Product
NGINX Open Source
Classifications
CWE-476, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 24, 2026CVE publishedPublication date reported by the CVE source.
  2. Mar 24, 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=0.5.15 <1.28.3
  2. Affected versionversion=1.29.0 <1.29.7

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

F5 Networks · NGINX Open Sourceversion=0.5.15 <1.28.3; version=1.29.0 <1.29.7
F5 Networks · NGINX Plusversion=R32 <R32 P5; version=R33 <*; version=R34 <*; version=R35 <R35 P2; version=R36 <R36 P3

Published CVSS scores

8.7F5 NetworksCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
7.5F5 NetworksCVSS:3.1/AV:N/AC:L/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-476NULL Pointer Dereference
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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