CVE-2026-28753

MEDIUMCVSS 6.3/10EPSS 0.26%

Last modified

CVE-2026-28753 is a medium-severity vulnerability rated 6.3/10 on the CVSS scale. 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. EPSS estimates a 0.26% chance of exploitation in the next 30 days.

Description

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.

Metrics

Weakness Enumeration

Affected Software

VendorProductVersionsUpdate
F5Nginx Plusr32P1
F5Nginx Plusr33—
F5Nginx Plusr34—
F5Nginx Plusr35—
F5Nginx Plusr36—
F5Nginx Open Source>= 0.6.27, <= 0.9.7—
F5Nginx Open Source>= 1.0.0, < 1.28.3—
F5Nginx Open Source>= 1.29.0, < 1.29.7—

References

Timeline

Published
Last Modified
Status
Analyzed

Frequently Asked Questions

What is CVE-2026-28753?
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.
How severe is CVE-2026-28753?
CVE-2026-28753 has a CVSS score of 6.3/10 (MEDIUM severity). The EPSS model estimates a 0.26% probability of exploitation in the next 30 days.
How do I fix CVE-2026-28753?
Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

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Source: NVD / NIST