# CVE-2025-4035: Libsoup: cookie domain validation bypass via uppercase characters in libsoup

> Attackers can bypass public suffix protections to set cookies for unauthorized domains, enabling session fixation attacks.

- **Severity:** Medium 4.3 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 29 Apr 2025
- **Updated:** 30 Jun 2026
- **Also known as:** AZL-61665, AZL-61670, DEBIAN-CVE-2025-4035, ECHO-bb6e-a23a-d95a, GHSA-9685-44wp-34gm, ROOT-OS-DEBIAN-13-CVE-2025-4035, UBUNTU-CVE-2025-4035

## What is CVE-2025-4035?

CVE-2025-4035 is a medium-severity vulnerability in Red Hat Enterprise Linux 10, published on 29 Apr 2025. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

### Official description

A flaw was found in libsoup. When handling cookies, libsoup clients mistakenly allow cookies to be set for public suffix domains if the domain contains at least two components and includes an uppercase character. This bypasses public suffix protections and could allow a malicious website to set cookies for domains it does not own, potentially leading to integrity issues such as session fixation.

Weakness: CWE-178 (Improper Handling of Case Sensitivity)

## Which versions are affected by CVE-2025-4035?


## How do I fix CVE-2025-4035?

Apply the vendor's patch.

## Is CVE-2025-4035 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2025-4035 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2025-4035 and fix it if it is affected.

What it is: CVE-2025-4035 is a medium-severity vulnerability in Red Hat Enterprise Linux 10, published on 29 Apr 2025. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2025-4035 exists.

Affected product: Red Hat Enterprise Linux 10. 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-2025-4035/ (Markdown: https://insights.sbomify.com/CVE-2025-4035/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2025-4035
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-4035
- OSV: https://osv.dev/vulnerability/CVE-2025-4035

---
From sbomify Insights: https://insights.sbomify.com/CVE-2025-4035/
Summaries are generated and may contain mistakes; the official description above is the record.