Cyber Resilience

CVE-2026-28753

F5 Nginx Plus r32 … r36

Published
24 March 2026
Modified
26 March 2026
Patch / advisory
View advisory
CVSS Score v4 6.3
Click a component to see what it means
Raw vectorCVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
EPSS Score 0.0026 18th percentile
Risk Priority 30 floored blend · peak EPSS

Summary

CVE-2026-28753 is a medium-severity CRLF Injection (CWE-93) vulnerability in F5 Nginx Plus. Its CVSS base score is 6.3 (Medium).

Operationally, exploitation aligns with the MITRE ATT&CK technique Content Injection (T1659); ranked at the 18th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.

The strongest mitigations our analysis identified map to SI-10 (Information Input Validation) — see the control section below for these in your framework.

OWASP Top 10 for Web (2025)

A05:2025 Injection

EU & UK References

Vulnerability Data

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…

more

potential request manipulation. Note: Software versions which have reached End of Technical Support (EoTS) are not evaluated.

CWE(s)
CWE-93

Related Threats

MITRE ATT&CK Enterprise Techniques

T1659 Content Injection Initial Access
Adversaries may gain access and continuously communicate with victims by injecting malicious content into systems through online network traffic.
attack.mitre.org →
T1190 Exploit Public-Facing Application Initial Access
Adversaries may attempt to exploit a weakness in an Internet-facing host or system to initially access a network.
attack.mitre.org →
Derived from this CVE’s CWE(s) via the direct CWE→ATT&CK cross-walk.

CVEs Like This One

CVE-2026-27654Same product: F5 Nginx Open Source
CVE-2024-24990Same product: F5 Nginx Open Source
CVE-2025-53859Same product: F5 Nginx Open Source
CVE-2026-32647Same product: F5 Nginx Open Source
CVE-2024-7347Same product: F5 Nginx Open Source
CVE-2026-27651Same product: F5 Nginx Open Source
CVE-2024-24989Same product: F5 Nginx Open Source
CVE-2026-27784Same product: F5 Nginx Open Source
CVE-2024-39792Same product: F5 Nginx Plus
CVE-2026-1642Same product: F5 Nginx Open Source

Affected Assets

f5
nginx plus
r32, r33, r34, r35, r36
f5
nginx open source
0.6.27 — 0.9.7 · 1.0.0 — 1.28.3 · 1.29.0 — 1.29.7

Mitigating Controls

Control response

Prevent
Stop it (NIST 800-53)

—

Detect
Catch it (NIST detect / respond)

—

Harden
Shrink the surface (DISA STIG)

—

Validate
Prove the fix (OWASP ASVS)
  • V4.2.4

Mitigating Controls (NIST 800-53 r5) AI

SI-10 Information Input Validation good match

Input validation directly stops untrusted data containing CRLF sequences from reaching the component that treats CRLF as a delimiter.

Mitigating Controls (NIST CSF 2.0) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.

PR.PS-06 mostly match
prevents

Secure SDLC practices directly require input neutralization and validation to block CRLF injection.

Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.

A.8.29 Security testing in development and acceptance mostly match
finds

Security testing can detect CRLF flaws but does not itself implement the neutralization.

A.8.25 Secure development life cycle partial match
prevents

Secure development lifecycle mandates input validation and output encoding that directly prevents CRLF injection.

A.8.26 Application security requirements partial match
prevents

Application security requirements include rules for neutralizing special characters such as CRLF in inputs.

A.8.27 Secure system architecture and engineering principles partial match
prevents

Secure architecture principles encourage safe handling of untrusted data but do not prescribe specific CRLF controls.

A.8.28 Secure coding partial match
prevents

Secure coding standards explicitly require neutralization of CRLF sequences, fully addressing this weakness.

References