CVE-2026-28753 | NGINX ngx_mail_proxy_module vulnerability

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.

Published: 2026-03-24 Last update: 2026-03-26 Assigner: [email protected] Source: [email protected]
NVD Status：Analyzed，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2026-28753 is rated Low Risk (26.6/100): CVSS Medium severity, with low exploitation likelihood (EPSS 0.02%). Monitor for updates and reassess as exploit intelligence or EPSS changes.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2026-28753

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-03-25 — 0.02% —

Full EPSS history (1 record total)

Common vulnerability scoring system (CVSS) metrics for CVE-2026-28753

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
6.3 4.0 MEDIUM
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/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 Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network.
Attack complexity (AC:H)
Exploitation depends on constrained or hard-to-reproduce conditions.
Attack requirements (AT:P)
Additional preconditions must be present for exploitation.
Privileges required (PR:N)
No privileges are required.
User interaction (UI:N)
No user interaction is required.
Vulnerable system confidentiality impact (VC:N)
No confidentiality impact on the vulnerable system.
Vulnerable system integrity impact (VI:L)
Limited integrity impact on the vulnerable system.
Vulnerable system availability impact (VA:N)
No availability impact on the vulnerable system.
Subsequent system confidentiality impact (SC:N)
No confidentiality impact on subsequent systems.
Subsequent system integrity impact (SI:N)
No integrity impact on subsequent systems.
Subsequent system availability impact (SA:N)
No availability impact on subsequent systems.
Exploit maturity (threat) (E:X)
Not defined: no reliable threat intelligence; scoring assumes the worst case (equivalent to Attacked).
Confidentiality requirement (CR:X)
Not defined: insufficient information; scoring treats this like High (worst case).
Integrity requirement (IR:X)
Not defined: insufficient information; scoring treats this like High (worst case).
Availability requirement (AR:X)
Not defined: insufficient information; scoring treats this like High (worst case).
Modified attack vector (MAV:X)
Not defined: scoring uses the Base Attack Vector (AV).
Modified attack complexity (MAC:X)
Not defined: scoring uses the Base Attack Complexity (AC).
Modified attack requirements (MAT:X)
Not defined: scoring uses the Base Attack Requirements (AT).
Modified privileges required (MPR:X)
Not defined: scoring uses the Base Privileges Required (PR).
Modified user interaction (MUI:X)
Not defined: scoring uses the Base User Interaction (UI).
Modified vulnerable system confidentiality impact (MVC:X)
Not defined: scoring uses the Base VC metric.
Modified vulnerable system integrity impact (MVI:X)
Not defined: scoring uses the Base VI metric.
Modified vulnerable system availability impact (MVA:X)
Not defined: scoring uses the Base VA metric.
Modified subsequent system confidentiality impact (MSC:X)
Not defined: scoring uses the Base SC metric.
Modified subsequent system integrity impact (MSI:X)
Not defined: scoring uses the Base SI metric.
Modified subsequent system availability impact (MSA:X)
Not defined: scoring uses the Base SA metric.
Safety (supplemental) (S:X)
Not evaluated.
Automatable (supplemental) (AU:X)
Not evaluated.
Recovery (supplemental) (R:X)
Not evaluated.
Value density (supplemental) (V:X)
Not evaluated.
Vulnerability response effort (supplemental) (RE:X)
Not evaluated.
Provider urgency (supplemental) (U:X)
Not evaluated.
 — — [email protected]
3.7 3.1 LOW
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:H)
Even with access, the exploit needs extra luck, timing, or a fussy environment to actually work.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:L)
Attackers could change some data, but it’s limited—not everything goes.
Availability (A:N)
Service keeps running; no real outage angle.
 2.2 1.4 [email protected]

Weakness enumeration for CVE-2026-28753

OS Trackers for CVE-2026-28753

vendor priority summary link
alpine — CVE-2026-28753: 1 source package rows (nginx); 3 state rows across 3 repos (3.22-main, 3.23-main, edge-main); fixed 3, open 0. https://security.alpinelinux.org/vuln/CVE-2026-28753
debian not yet assigned CVE-2026-28753 not yet assigned priority: Debian including 1 source packages (nginx), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5. https://security-tracker.debian.org/tracker/CVE-2026-28753
redhat low — https://access.redhat.com/security/cve/CVE-2026-28753
suse low CVE-2026-28753 severity low: SUSE including 2 source package names (nginx-1.29.7-1.1, nginx-source-1.29.7-1.1), 2 product×package rows across 1 product lines (openSUSE Tumbleweed): Fixed 2. https://www.suse.com/security/cve/CVE-2026-28753/
ubuntu medium CVE-2026-28753 medium priority: Ubuntu including 1 source packages (nginx), 9 status rows across 9 suites (bionic, focal, jammy, noble, questing, resolute, trusty, upstream, xenial): needs-triage 4, released 4, not-affected 1. https://ubuntu.com/security/CVE-2026-28753

Affected software / configurations for CVE-2026-28753

Vendor Product Version Raw CPE
f5 nginx_plus r32 cpe:2.3:a:f5:nginx_plus:r32:p1:*:*:*:*:*:*
f5 nginx_plus r32 cpe:2.3:a:f5:nginx_plus:r32:p2:*:*:*:*:*:*
f5 nginx_plus r32 cpe:2.3:a:f5:nginx_plus:r32:p3:*:*:*:*:*:*
f5 nginx_plus r32 cpe:2.3:a:f5:nginx_plus:r32:p4:*:*:*:*:*:*
f5 nginx_plus r33 cpe:2.3:a:f5:nginx_plus:r33:*:*:*:*:*:*:*
f5 nginx_plus r33 cpe:2.3:a:f5:nginx_plus:r33:p1:*:*:*:*:*:*
f5 nginx_plus r33 cpe:2.3:a:f5:nginx_plus:r33:p2:*:*:*:*:*:*
f5 nginx_plus r33 cpe:2.3:a:f5:nginx_plus:r33:p3:*:*:*:*:*:*
f5 nginx_plus r34 cpe:2.3:a:f5:nginx_plus:r34:*:*:*:*:*:*:*
f5 nginx_plus r34 cpe:2.3:a:f5:nginx_plus:r34:p1:*:*:*:*:*:*
f5 nginx_plus r34 cpe:2.3:a:f5:nginx_plus:r34:p2:*:*:*:*:*:*
f5 nginx_plus r35 cpe:2.3:a:f5:nginx_plus:r35:*:*:*:*:*:*:*
f5 nginx_plus r35 cpe:2.3:a:f5:nginx_plus:r35:p1:*:*:*:*:*:*
f5 nginx_plus r36 cpe:2.3:a:f5:nginx_plus:r36:*:*:*:*:*:*:*
f5 nginx_plus r36 cpe:2.3:a:f5:nginx_plus:r36:p1:*:*:*:*:*:*
f5 nginx_plus r36 cpe:2.3:a:f5:nginx_plus:r36:p2:*:*:*:*:*:*
f5 nginx_open_source >= 0.6.27, <= 0.9.7 cpe:2.3:a:f5:nginx_open_source:*:*:*:*:*:*:*:*
f5 nginx_open_source >= 1.0.0, < 1.28.3 cpe:2.3:a:f5:nginx_open_source:*:*:*:*:*:*:*:*
f5 nginx_open_source >= 1.29.0, < 1.29.7 cpe:2.3:a:f5:nginx_open_source:*:*:*:*:*:*:*:*

References for CVE-2026-28753

cvelogic Threat Intelligence