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NVD / CVE Program· CNA f5

CVE-2025-53859: NGINX ngx_mail_smtp_module vulnerability

Noroxi assessment

Priority: Monitor (action score 25/100)

  • The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
  • Probability of exploitation in the next 30 days: 0.43% (FIRST EPSS).
  • Anyone who can reach it over the internet can trigger it. No account or password is required. No user action is required. No special conditions are required; it is repeatable.
  • Fixed version: azl3 nginx 1.25.4-4 on Azure Linux 3.0 1.25.4-5; azl3 nginx 1.25.4-5 on Azure Linux 3.0 1.25.4-5; cbl2 nginx 1.22.1-13 on CBL Mariner 2.0 1.22.1-14.
  • Severity is disputed: the assigning authority (CNA) scores it 3.7, NVD 6.3.

Low priority for now. Upgrade to azl3 nginx 1.25.4-4 on Azure Linux 3.0 1.25.4-5; azl3 nginx 1.25.4-5 on Azure Linux 3.0 1.25.4-5; cbl2 nginx 1.22.1-13 on CBL Mariner 2.0 1.22.1-14 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

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.

MediumCVSS 6.3 · v4.0—No exploit Fix available
Published
Aug 13, 2025
Updated
Jun 17, 2026
EPSS
0.4% · 38th percentile

Report tools

JSON

Action score

25

Monitor

Low priority for now.

CVSS
25 / 40 · 6.3 / 10
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.4%

CISA SSVC decision

Exploitation
none
Automatable
no
Technical impact
partial

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD
—
CNA · f5
3.7
NVD has not scored this yet; the score shown is the CNA’s.

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

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

Get told when this record changes

  • Not in KEV: no record of exploitation in the wild
  • No public exploit code on record
  • A fix has been released

If any of these changes, we'll tell you in the daily email digest.

Follow CVE-2025-53859

When you'll hear from us

  • when it enters CISA KEV
  • when exploit code appears or is weaponized
  • when the record is updated (including a fixed version)
  • when EPSS rises 20 points in a week

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

VendorProduct
f5nginx plus
f5nginx open source

Using nginx plus? Add it to your stack and be the first to know about CVEs like this one. (Nginx)

Watch new CVEs for nginx plus

When you'll hear from us

  • when a new CVE affecting this product is published
  • when a record in your stack enters KEV or gets exploit code

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Running WordPress? Scan your site free with WP Lens

  • Stack alerts: add the products and versions you run, get the new CVEs that affect them
  • Uptime monitoring: 1 site, instant email when it goes down
  • Add your domain: subdomains and takeover risk scanned every week (1 domain)
  • 10 scans an hour on the security tools (3 a day without an account), an API key and MCP
  • All your scans in one panel: findings, what changed in the last scan, a report per domain or per client (PDF, share link)
All free tools

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Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

  • f5 nginx open source0.7.22 and later · before 1.29.1
  • f5 nginx plusr30
  • f5 nginx plusr31
  • f5 nginx plusr32
  • f5 nginx plusr33
  • f5 nginx plusr34

Versions reported by the vendor

Affected version ranges reported by the assigning authority (f5). Independent of NVD's CPE analysis and usually ahead of it.

  • F5 NGINX Open Source

    • 0.7 and later · before 1.29.1affected

  • F5 NGINX Plus

    • R35not affected
    • R34 and later · before R34 P2affected
    • R33 and later · before R33 P3affected
    • R32 and later · before R32 P3affected
    • R31 and lateraffected
    • R30 and lateraffected

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

EcosystemPackageAffected rangeFix
Alpine:v3.22nginxbefore 1.28.2-r01.28.2-r0
Debian:12nginxbefore 1.22.1-9+deb12u31.22.1-9+deb12u3
Debian:13nginxbefore 1.26.3-3+deb13u11.26.3-3+deb13u1
Debian:14nginxbefore 1.28.0-31.28.0-3
openSUSE:Tumbleweednginxbefore 1.29.1-1.11.29.1-1.1
Red Hat:hummingbird:1nginxbefore 0:1.30.0-1.hum10:1.30.0-1.hum1
Red Hat:hummingbird:1nginx-all-modulesbefore 0:1.30.0-1.hum10:1.30.0-1.hum1
Red Hat:hummingbird:1nginx-corebefore 0:1.30.0-1.hum10:1.30.0-1.hum1
Red Hat:hummingbird:1nginx-filesystembefore 0:1.30.0-1.hum10:1.30.0-1.hum1
Red Hat:hummingbird:1nginx-mod-develbefore 0:1.30.0-1.hum10:1.30.0-1.hum1
Red Hat:hummingbird:1nginx-mod-http-geoipbefore 0:1.30.0-1.hum10:1.30.0-1.hum1
Red Hat:hummingbird:1nginx-mod-http-image-filterbefore 0:1.30.0-1.hum10:1.30.0-1.hum1
Red Hat:hummingbird:1nginx-mod-http-perlbefore 0:1.30.0-1.hum10:1.30.0-1.hum1
Red Hat:hummingbird:1nginx-mod-http-xslt-filterbefore 0:1.30.0-1.hum10:1.30.0-1.hum1
Red Hat:hummingbird:1nginx-mod-mailbefore 0:1.30.0-1.hum10:1.30.0-1.hum1
Red Hat:hummingbird:1nginx-mod-streambefore 0:1.30.0-1.hum10:1.30.0-1.hum1
Red Hat:hummingbird:1nginx-mod-stream-geoipbefore 0:1.30.0-1.hum10:1.30.0-1.hum1

Same product

f5: all records

Other highest-scoring records for the same primary product.

Published before and after this one in the same product

  • ← EarlierCVE-2024-39792Aug 14, 2024 · NGINX Plus MQTT vulnerability
    34Monitor
  • Later →CVE-2026-28753Mar 24, 2026 · NGINX ngx_mail_proxy_module vulnerability
    25Monitor
  • Later →CVE-2026-28755Mar 24, 2026 · NGINX ngx_stream_ssl_module vulnerability
    21Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / packageFixed versionSource
azl3 nginx 1.25.4-4 on Azure Linux 3.01.25.4-5 · CBL-Mariner ReleasesMicrosoft (MSRC)
azl3 nginx 1.25.4-5 on Azure Linux 3.01.25.4-5 · CBL-Mariner ReleasesMicrosoft (MSRC)
cbl2 nginx 1.22.1-13 on CBL Mariner 2.01.22.1-14 · CBL-Mariner ReleasesMicrosoft (MSRC)
cbl2 nginx 1.22.1-14 on CBL Mariner 2.01.22.1-14 · CBL-Mariner ReleasesMicrosoft (MSRC)
alpine:nginx1.28.2-r0 · Alpine:v3.22Package registry (OSV)
debian:nginx1.22.1-9+deb12u3 · Debian:12Package registry (OSV)
opensuse:nginx1.29.1-1.1 · openSUSE:TumbleweedPackage registry (OSV)
red hat:nginx0:1.30.0-1.hum1 · Red Hat:hummingbird:1Package registry (OSV)
red hat:nginx-all-modules0:1.30.0-1.hum1 · Red Hat:hummingbird:1Package registry (OSV)
red hat:nginx-core0:1.30.0-1.hum1 · Red Hat:hummingbird:1Package registry (OSV)
red hat:nginx-filesystem0:1.30.0-1.hum1 · Red Hat:hummingbird:1Package registry (OSV)
red hat:nginx-mod-devel0:1.30.0-1.hum1 · Red Hat:hummingbird:1Package registry (OSV)
red hat:nginx-mod-http-geoip0:1.30.0-1.hum1 · Red Hat:hummingbird:1Package registry (OSV)
red hat:nginx-mod-http-image-filter0:1.30.0-1.hum1 · Red Hat:hummingbird:1Package registry (OSV)
red hat:nginx-mod-http-perl0:1.30.0-1.hum1 · Red Hat:hummingbird:1Package registry (OSV)
red hat:nginx-mod-http-xslt-filter0:1.30.0-1.hum1 · Red Hat:hummingbird:1Package registry (OSV)
red hat:nginx-mod-mail0:1.30.0-1.hum1 · Red Hat:hummingbird:1Package registry (OSV)
red hat:nginx-mod-stream0:1.30.0-1.hum1 · Red Hat:hummingbird:1Package registry (OSV)
red hat:nginx-mod-stream-geoip0:1.30.0-1.hum1 · Red Hat:hummingbird:1Package registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

No history yet (it accumulates with the daily EPSS job).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

No commit or PR link among the references.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

  • CVE-2026-32647223 days apartNGINX ngx_http_mp4_module vulnerability
    34Monitor

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

Technical details

Attack conditions

  • Anyone who can reach it over the internet can trigger it.
  • No account or password is required.
  • No user action is required.
  • No special conditions are required; it is repeatable.

If successful

Confidentiality
Integrity
Availability
Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
X

Weakness class (CWE)

CWE-125 · Out-of-bounds Read

CVSS vector

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

nvd-secondary

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

ATT&CK techniques

—

Change log

  1. Fix✗ → ✓

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References

Show all references (1 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records