How severe is CVE-2025-12642?

CVE-2025-12642 has a CVSS 3.x base score of 9.1, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability none.

Is CVE-2025-12642 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (26th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2025-12642?

CVE-2025-12642 affects Lighttpd. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2025-12642?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.

Does CVE-2025-12642 have an EU (EUVD) identifier?

Yes. CVE-2025-12642 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2025-37517.

When was CVE-2025-12642 published?

CVE-2025-12642 was published on 2025-11-03 and last updated on 2026-06-17.

CVE-2025-12642

CVE-2025-12642 is a critical-severity vulnerability in Lighttpd with a CVSS 3.x base score of 9.1. 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-444.

Key facts

Severity: Critical (CVSS 3.x base score 9.1)
CVSS v4: 6.9
EPSS exploit prediction: 0% (26th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2025-37517
Weakness: CWE-444
Affected product: Lighttpd
Published: 2025-11-03
Last modified: 2026-06-17

Description

lighttpd1.4.80 incorrectly merged trailer fields into headers after http request parsing. This behavior can be exploited to conduct HTTP Header Smuggling attacks. Successful exploitation may allow an attacker to: * Bypass access control rules * Inject unsafe input into backend logic that trusts request headers * Execute HTTP Request Smuggling attacks under some conditions This issue affects lighttpd1.4.80

Frequently asked questions

What is CVE-2025-12642?: lighttpd1.4.80 incorrectly merged trailer fields into headers after http request parsing. This behavior can be exploited to conduct HTTP Header Smuggling attacks. Successful exploitation may allow an attacker to: * Bypass access control rules * Inject unsafe input into backend logic that trusts request headers * Execute HTTP Request Smuggling attacks under some conditions This issue affects lighttpd1.4.80
How severe is CVE-2025-12642?: CVE-2025-12642 has a CVSS 3.x base score of 9.1, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability none.
Is CVE-2025-12642 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (26th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2025-12642?: CVE-2025-12642 affects Lighttpd. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2025-12642?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.
Does CVE-2025-12642 have an EU (EUVD) identifier?: Yes. CVE-2025-12642 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2025-37517.
When was CVE-2025-12642 published?: CVE-2025-12642 was published on 2025-11-03 and last updated on 2026-06-17.

References

https://github.com/lighttpd/lighttpd1.4/commit/35cb89c103877de62d6b63d0804255475d77e5e1

Affected products (1)

cpe:2.3:a:lighttpd:lighttpd:1.4.80:*:*:*:*:*:*:*

More vulnerabilities in Lighttpd

CVE-2019-11072 — Critical (CVSS 9.8): lighttpd before 1.4.54 has a signed integer overflow, which might allow remote attackers to cause a denial of service…
CVE-2014-2323 — Critical (CVSS 9.8): SQL injection vulnerability in mod_mysql_vhost.c in lighttpd before 1.4.35 allows remote attackers to execute arbitrary…
CVE-2007-3949 — High (CVSS 8.3): mod_access.c in lighttpd 1.4.15 ignores trailing / (slash) characters in the URL, which allows remote attackers to…
CVE-2007-1870 — High (CVSS 7.8): lighttpd before 1.4.14 allows attackers to cause a denial of service (crash) via a request to a file whose mtime is 0,…
CVE-2013-4559 — High (CVSS 7.6): lighttpd before 1.4.33 does not check the return value of the (1) setuid, (2) setgid, or (3) setgroups functions, which…
CVE-2022-41556 — High (CVSS 7.5): A resource leak in gw_backend.c in lighttpd 1.4.56 through 1.4.66 could lead to a denial of service (connection-slot…

All CVEs affecting Lighttpd →

Other CWE-444 (HTTP Request/Response Smuggling) vulnerabilities

CVE-2025-1867 — Critical (CVSS 10.0): Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling') vulnerability in ithewei libhv allows…
CVE-2022-22536 — Critical (CVSS 10.0): SAP NetWeaver Application Server ABAP, SAP NetWeaver Application Server Java, ABAP Platform, SAP Content Server 7.53…
CVE-2018-3907 — Critical (CVSS 10.0): An exploitable vulnerability exists in the REST parser of video-core's HTTP server of the Samsung SmartThings Hub…
CVE-2025-55315 — Critical (CVSS 9.9): Inconsistent interpretation of http requests ('http request/response smuggling') in ASP.NET Core allows an authorized…
CVE-2020-15049 — Critical (CVSS 9.9): An issue was discovered in http/ContentLengthInterpreter.cc in Squid before 4.12 and 5.x before 5.0.3. A Request…
CVE-2026-13763 — Critical (CVSS 9.8): Inconsistent interpretation of HTTP/2 requests in AWS Application Load Balancer with AWS WAF enabled might allow remote…

Browse all CWE-444 (HTTP Request/Response Smuggling) vulnerabilities →