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Vulnerabilities

Vulnerability · 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.

Published Mar 24, 2026 · catalog updated Jun 17, 2026 · nginx plus

Check if you run it

No confirmed exploitation is on record for CVE-2026-28753. EPSS is 0.26%. Act only if a listed version of nginx plus is installed.

Gaps on this record

  • No version range is stored. A customer cannot check an installed version against this record.
  • No vendor fix or required action is stored. Compare the linked advisory before you change production.
Severity
Medium6.3
Known exploitation
Not in CISA/VulnCheck KEV
EPSS
0.26%
Remediation
Advisory link
Affected products
cpe f5/nginx open source · cpe f5/nginx plus

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.

Are you affected?

Enter the version you run. The result uses only the ranges stored on this record.

The check returns affected, not affected, or incomplete. It does not guess a version that is missing from the record.

  • cpe f5/nginx open sourceversion unspecified
  • cpe f5/nginx plusr32
  • cpe f5/nginx plusr33

How to fix CVE-2026-28753

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Should you patch?

No confirmed exploitation is on record for CVE-2026-28753. EPSS is 0.26%. Act only if a listed version of nginx plus is installed.

Which versions are affected?

Compare what you have installed with f5/nginx plus r32; f5/nginx plus r33. Compare the installed version with the linked vendor advisory before you change production.

What should an analyst verify?

CWE-93. EPSS 0.26%. There is no CISA KEV listing. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.

Technology hubs

Nginx security

Code

The project this record applies to. Exploit listings stay in References.

No public source repository is identified for this product.

Timeline

Detection, updates, and resolution for this record.

  1. Mar 24, 2026 · NIST NVD

    Detected

    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.

  2. Jun 17, 2026 · NIST NVD

    Updated

    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.

Sources

  • CVE.orgVulnerability recordCVE-2026-28753

    Official CVE identifier

    cve.org
  • FIRST EPSSExploitation probabilityCVE-2026-28753

    30-day exploitation probability 0.3%

    first.org
  • NIST NVDVulnerability recordCVE-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 re

    nvd.nist.gov

References

Freshness

Last verified in this catalog Oct 18, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.