CVE-2025-53859
CVE-2025-53859 is a low-severity vulnerability in F5 Nginx Plus with a CVSS 3.x base score of 3.7. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-125.
Key facts
- Severity: Low (CVSS 3.x base score 3.7)
- CVSS v4: 6.3
- EPSS exploit prediction: 0% (29th percentile)
- Actively exploited: Not listed in CISA KEV
- EU (EUVD) id: EUVD-2025-24579
- Weakness: CWE-125
- Affected product: F5 Nginx Plus
- Published:
- Last modified:
Description
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.
Frequently asked questions
- What is CVE-2025-53859?
- 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.
- How severe is CVE-2025-53859?
- CVE-2025-53859 has a CVSS 3.x base score of 3.7, rated low severity. It is exploitable over network with high attack complexity, requires no privileges and no user interaction. Impact on confidentiality is low, integrity none, and availability none.
- Is CVE-2025-53859 being actively exploited?
- It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (29th percentile), an estimate of the probability of exploitation in the next 30 days.
- What products are affected by CVE-2025-53859?
- CVE-2025-53859 primarily affects F5 Nginx Plus. In total, 11 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
- How do I fix CVE-2025-53859?
- Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
- Does CVE-2025-53859 have an EU (EUVD) identifier?
- Yes. CVE-2025-53859 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2025-24579.
- When was CVE-2025-53859 published?
- CVE-2025-53859 was published on 2025-08-13 and last updated on 2026-06-17.
References
- https://my.f5.com/manage/s/article/K000152786
- http://www.openwall.com/lists/oss-security/2025/08/13/5
Affected products (11)
- cpe:2.3:a:f5:nginx_plus:r30:-:*:*:*:*:*:*
- cpe:2.3:a:f5:nginx_plus:r31:-:*:*:*:*:*:*
- cpe:2.3:a:f5:nginx_plus:r32:-:*:*:*:*:*:*
- cpe:2.3:a:f5:nginx_plus:r32:p1:*:*:*:*:*:*
- cpe:2.3:a:f5:nginx_plus:r32:p2:*:*:*:*:*:*
- cpe:2.3:a:f5:nginx_plus:r33:-:*:*:*:*:*:*
- cpe:2.3:a:f5:nginx_plus:r33:p1:*:*:*:*:*:*
- cpe:2.3:a:f5:nginx_plus:r33:p2:*:*:*:*:*:*
- cpe:2.3:a:f5:nginx_plus:r34:-:*:*:*:*:*:*
- cpe:2.3:a:f5:nginx_plus:r34:p1:*:*:*:*:*:*
- cpe:2.3:a:f5:nginx_open_source:*:*:*:*:*:*:*:*
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