CVE-2026-28753
CRLF Injection in NGINX ngx_mail_smtp_module Enables Request Manipulation
Publication date: 2026-03-24
Last updated on: 2026-03-26
Assigner: F5 Networks
Description
Description
CVSS Scores
EPSS Scores
| Probability: | |
| Percentile: |
Meta Information
Affected Vendors & Products
| Vendor | Product | Version / Range |
|---|---|---|
| f5 | nginx_plus | r32 |
| f5 | nginx_plus | r32 |
| f5 | nginx_plus | r33 |
| f5 | nginx_plus | r33 |
| f5 | nginx_plus | r34 |
| f5 | nginx_plus | r32 |
| f5 | nginx_plus | r33 |
| f5 | nginx_plus | r34 |
| f5 | nginx_plus | r36 |
| f5 | nginx_plus | r33 |
| f5 | nginx_plus | r34 |
| f5 | nginx_plus | r35 |
| f5 | nginx_plus | r36 |
| f5 | nginx_plus | r36 |
| f5 | nginx_plus | r32 |
| f5 | nginx_plus | r35 |
| f5 | nginx_open_source | From 1.29.0 (inc) to 1.29.7 (exc) |
| f5 | nginx_open_source | From 0.6.27 (inc) to 0.9.7 (inc) |
| f5 | nginx_open_source | From 1.0.0 (inc) to 1.28.3 (exc) |
Helpful Resources
Exploitability
| CWE ID | Description |
|---|---|
| CWE-93 | The product 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. |
Attack-Flow Graph
AI Powered Q&A
Can you explain this vulnerability to me?
This vulnerability exists in the ngx_mail_smtp_module of NGINX Plus and NGINX Open Source. It is caused by improper handling of CRLF (Carriage Return Line Feed) sequences in DNS responses. An attacker who controls a DNS server can exploit this flaw to inject arbitrary headers into SMTP upstream requests, which can manipulate the requests being sent.
How can this vulnerability impact me? :
The vulnerability allows an attacker to manipulate SMTP upstream requests by injecting arbitrary headers. This could lead to unauthorized modification of email communications or disruption of mail services. However, the CVSS scores indicate a low to medium severity impact, with no confidentiality or availability impact but a low integrity impact.
How does this vulnerability affect compliance with common standards and regulations (like GDPR, HIPAA)?:
I don't know
How can this vulnerability be detected on my network or system? Can you suggest some commands?
I don't know
What immediate steps should I take to mitigate this vulnerability?
I don't know