What is CVE-2026-28753?

CVE-2026-28753 is a low-severity vulnerability in F5 Nginx Open Source, classified under CRLF Injection. CVSS score: 3.7/10. Published 2026-03-24.

How severe is CVE-2026-28753?

Low severity. CVSS v3 base score is 3.7 out of 10.

Vulnerability in F5 Nginx Open Source

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.

Vulnerability class: CRLF Injection

EPSS: 0.003 (18.2th percentile) — read the EPSS interpretation.

CVSS v3 metric

CVSS v3 base score 3.7 (Low). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N.

Affected products

F5 Nginx Open Source — versions 1.29.0, 0.6.27
F5 Nginx_open_source
F5 Nginx Plus — versions R36, R35, R34
F5 Nginx_plus — versions r32, r33, r34

Weakness classification (CWE)

CWE-93 — CRLF Injection

References

f5sirt@f5.com (vendor-advisory, Vendor Advisory)

Frequently asked questions

What is CVE-2026-28753?: CVE-2026-28753 is a low-severity vulnerability in F5 Nginx Open Source, classified under CRLF Injection. CVSS score: 3.7/10. Published 2026-03-24.
How severe is CVE-2026-28753?: Low severity. CVSS v3 base score is 3.7 out of 10.