CVE-2025-53859 | NGINX ngx_mail_smtp_module vulnerability

NGINX Open Source and NGINX Plus have a vulnerability in the ngx_mail_smtp_module that might allow an unauthenticated attacker to over-read NGINX SMTP authentication process memory; as a result, the server side may leak arbitrary bytes sent in a request to the authentication server. This issue happens during the NGINX SMTP authentication process and requires the attacker to make preparations against the target system to extract the leaked data. The issue affects NGINX only if (1) it is built with the ngx_mail_smtp_module, (2) the smtp_auth directive is configured with method "none," and (3) the authentication server returns the "Auth-Wait" response header. Note: Software versions which have reached End of Technical Support (EoTS) are not evaluated.

Published: 2025-08-13 Last update: 2025-11-04 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2025-53859 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-2025-53859

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 2026-01-18 0.06% 0.02% -0.04%
2 2026-01-10 0.04% 0.06% +0.02%
3 2026-01-09 — 0.04% —

Full EPSS history (6 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2025-53859

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:L/AT:P/PR:N/UI:N/VC:L/VI:N/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:L)
Exploitation conditions are straightforward and stable.
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:L)
Limited confidentiality impact on the vulnerable system.
Vulnerable system integrity impact (VI:N)
No 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:L/I:N/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:L)
Some sensitive info could get out, but not a total data dump.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:N)
Service keeps running; no real outage angle.
 2.2 1.4 [email protected]

Weakness enumeration for CVE-2025-53859

OS Trackers for CVE-2025-53859

vendor priority summary link
alpine low CVE-2025-53859: 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-2025-53859
debian not yet assigned CVE-2025-53859 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-2025-53859
redhat low — https://access.redhat.com/security/cve/CVE-2025-53859
suse low CVE-2025-53859 severity low: SUSE including 8 source package names (1.1.0-1.1:nginx-1.21.5-150600.10.12.1, 1.21.5-2.51:nginx-1.21.5-150600.10.12.1, …), 12 product×package rows across 7 product lines (Container private-registry/harbor-nginx, Container private-registry/harbor-portal, … (7 product lines)): Fixed 12. https://www.suse.com/security/cve/CVE-2025-53859/
ubuntu medium CVE-2025-53859 medium priority: Ubuntu including 1 source packages (nginx), 9 status rows across 9 suites (bionic, focal, jammy, noble, plucky, questing, trusty, upstream, xenial): needs-triage 5, released 4. https://ubuntu.com/security/CVE-2025-53859

Affected software / configurations for CVE-2025-53859

Vendor Product Version Raw CPE
f5 nginx_plus r30 cpe:2.3:a:f5:nginx_plus:r30:-:*:*:*:*:*:*
f5 nginx_plus r31 cpe:2.3:a:f5:nginx_plus:r31:-:*:*:*:*:*:*
f5 nginx_plus r32 cpe:2.3:a:f5:nginx_plus:r32:-:*:*:*:*:*:*
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 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 r34 cpe:2.3:a:f5:nginx_plus:r34:-:*:*:*:*:*:*
f5 nginx_plus r34 cpe:2.3:a:f5:nginx_plus:r34:p1:*:*:*:*:*:*
f5 nginx_open_source >= 0.7.22, < 1.29.1 cpe:2.3:a:f5:nginx_open_source:*:*:*:*:*:*:*:*

References for CVE-2025-53859

cvelogic Threat Intelligence