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CVE-2026-27651 is a NULL pointer dereference vulnerability in NGINX Open Source and NGINX Plus when the ngx_mail_auth_http_module module is enabled. The issue is triggered by crafted or otherwise undisclosed requests that reach the mail authentication flow under specific conditions: CRAM-MD5 or APOP authentication must be enabled, and the external authentication server must permit retry by returning the Auth-Wait response header. Successful triggering causes an NGINX worker process to terminate. Reported affected NGINX Open Source versions are 0.5.15 through 1.29.6; versions 1.29.7+ and 1.28.3+ are reported as not vulnerable. The weakness is classified as CWE-476.
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What an attacker gets, and what they’ve been doing with it.
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No public exploit code observed for this vulnerability.
Products and vendors Mallory has correlated with this vulnerability. Open in Mallory to drill down to specific CPE configurations and version ranges.
Vendor-confirmed product mapping. Mallory continuously reconciles this list against your asset inventory.
14 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
A denial-of-service vulnerability in the ngx_mail_auth_http_module of NGINX Plus and NGINX Open Source that can cause worker processes to terminate under specific mail authentication and retry conditions.
A vulnerability in nginx mail-related authentication handling affecting CRAM-MD5 or APOP authentication mechanisms.
Query your assets running an affected version, and investigate the blast radius.
Every observed campaign linking this CVE to a named adversary.
Malware families riding this exploit, with evidence and IOCs.
YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.
Cross-references every affected SKU, including bundled OEM variants.
Community discussion across Reddit, Mastodon, and other social sources.