CVE-2026-28753 PUBLISHED

NGINX ngx_mail_proxy_module vulnerability

Assigner: f5
Reserved: 18.03.2026 Published: 24.03.2026 Updated: 24.03.2026

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.

CVSS Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N
CVSS Score: 3.7

Attack Vector	Network	Scope	Unchanged
Attack Complexity	High	Confidentiality Impact	None
Privileges Required	None	Integrity Impact	Low
User Interaction	None	Availability Impact	None

CVSS 3.1

CVSS Vector: CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N
CVSS Score: 6.3

Exploitability Metrics		Vulnerable System Impact Metrics		Subsequent System Impact Metrics
Attack Vector	Network	Confidentiality	None	Confidentiality	None
Attack Complexity	High	Integrity	Low	Integrity	None
Attack Requirements	Present	Availability	None	Availability	None
Privileges Required	None
User Interaction	None

CVSS 4.0

Product Status

Vendor	F5
Product	NGINX Open Source
Versions	Default: unknown affected from 1.29.0 to 1.29.7 (excl.) affected from 0.6.27 to 1.28.3 (excl.)

Vendor	F5
Product	NGINX Plus
Versions	Default: unknown affected from R36 to R36 P3 (excl.) affected from R35 to R35 P2 (excl.) affected from R34 to * (excl.) affected from R33 to * (excl.) affected from R32 to R32 P5 (excl.)

Credits

Asim Viladi Oglu Manizada reporter
Colin Warren reporter
Xiao Liu (Yunnan University) reporter
Yuan Tan (UC Riverside) reporter
Bird Liu (Lanzhou University) reporter

References

https://my.f5.com/manage/s/article/K000160367

Problem Types

CWE-93 Improper Neutralization of CRLF Sequences ('CRLF Injection') CWE