# CVE-2025-12642: HTTP Header Smuggling via Trailer Merge

> Attackers can bypass access controls and inject malicious headers via HTTP header smuggling in lighttpd, potentially leading to backend logic manipulation.

- **Severity:** Medium 6.9 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:N/SI:L/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 3 Nov 2025
- **Updated:** 3 Nov 2025
- **Also known as:** GHSA-fvx8-q97q-cw73, UBUNTU-CVE-2025-12642

## What is CVE-2025-12642?

CVE-2025-12642 is a medium-severity vulnerability in lighttpd, published on 3 Nov 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official 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

Weakness: CWE-444 (Inconsistent Interpretation of HTTP Requests)

## Which versions are affected by CVE-2025-12642?

It affects 1 product.


Products: Lighttpd Lighttpd.

## How do I fix CVE-2025-12642?

No fix has been published for CVE-2025-12642 yet. Limit exposure of the affected software until one is available.

## Is CVE-2025-12642 being exploited?

There is no known exploitation of CVE-2025-12642 in the wild and no public exploit code.

## Other vulnerabilities in lighttpd

- [CVE-2019-11072](https://insights.sbomify.com/CVE-2019-11072/): Integer overflow in n/a (critical 9.8)
- [CVE-2007-3949](https://insights.sbomify.com/CVE-2007-3949/): Security feature bypass in n/a (high 8.3)
- [CVE-2007-1870](https://insights.sbomify.com/CVE-2007-1870/): Null dereference in n/a (high 7.8)
- [CVE-2022-30780](https://insights.sbomify.com/CVE-2022-30780/): Denial of service in n/a (high 7.5)
- [CVE-2007-4727](https://insights.sbomify.com/CVE-2007-4727/): Memory corruption in n/a (medium 6.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-12642 and fix it if it is affected.

What it is: CVE-2025-12642 is a medium-severity vulnerability in lighttpd, published on 3 Nov 2025. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2025-12642 in the wild and no public exploit code.

Affected product: lighttpd. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2025-12642/ (Markdown: https://insights.sbomify.com/CVE-2025-12642/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-12642
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-12642
- OSV: https://osv.dev/vulnerability/CVE-2025-12642

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-12642/
Summaries are generated and may contain mistakes; the official description above is the record.