NGINX ngx_mail_smtp_module CRLF Injection via DNS Response
CVE-2026-28753 Published on March 24, 2026
NGINX ngx_mail_proxy_module vulnerability
NGINX Plus and NGINX Open Source have a vulnerability in the ngx_mail_smtp_module module due to the improper handling of CRLF sequences in DNS responses. This allows an attacker-controlled DNS server to inject arbitrary headers into SMTP upstream requests, leading to potential request manipulation. Note: Software versions which have reached End of Technical Support (EoTS) are not evaluated.
Vulnerability Analysis
CVE-2026-28753 can be exploited with network access, and does not require authorization privileges or user interaction. This vulnerability is consided to have a high level of attack complexity. The potential impact of an exploit of this vulnerability is considered to have no impact on confidentiality, with no impact on integrity, and no impact on availability.
Weakness Type
What is a CRLF Injection Vulnerability?
The software uses CRLF (carriage return line feeds) as a special element, e.g. to separate lines or records, but it does not neutralize or incorrectly neutralizes CRLF sequences from inputs.
CVE-2026-28753 has been classified to as a CRLF Injection vulnerability or weakness.
Products Associated with CVE-2026-28753
stack.watch emails you whenever new vulnerabilities are published in F5 Networks Nginx Open Source or F5 Networks Nginx Plus. Just hit a watch button to start following.
Affected Versions
F5 NGINX Open Source:- Version 1.29.0 and below 1.29.7 is affected.
- Version 0.6.27 and below 1.28.3 is affected.
- Version R36 and below R36 P3 is affected.
- Version R35 and below R35 P2 is affected.
- Version R34 and below * is affected.
- Version R33 and below * is affected.
- Version R32 and below R32 P5 is affected.
Exploit Probability
EPSS (Exploit Prediction Scoring System) scores estimate the probability that a vulnerability will be exploited in the wild within the next 30 days. The percentile shows you how this score compares to all other vulnerabilities.