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
Published · last modified .
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.
EPSS exploit prediction
EPSS: 0.003 (17.7th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 18th percentile — 17.7% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.003 · newest: 0.003 · change: +0.000
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)
References
- my.f5.com/manage/s/article/K000160367 (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.