# CVE-2026-66339: Libsoup: libsoup: proxy credentials leak to destination server via proxy-authorization header in connect tunnels

> Attackers can capture proxy credentials when libsoup incorrectly sends Proxy-Authorization headers to destination servers over HTTPS tunnels.

- **Severity:** Medium 6.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/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:** 24 Jul 2026
- **Updated:** 28 Jul 2026
- **Also known as:** AZL-94098, DEBIAN-CVE-2026-66339, ECHO-3341-e81d-bf5b, GHSA-vh9q-f797-xwg7, UBUNTU-CVE-2026-66339

## What is CVE-2026-66339?

CVE-2026-66339 is a medium-severity vulnerability in Redhat Enterprise Linux, published on 24 Jul 2026. 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. After a CONNECT tunnel is established through an HTTP proxy, libsoup incorrectly attaches the Proxy-Authorization header to subsequent HTTPS requests sent through that tunnel to the destination server. This allows the destination server to capture proxy credentials, leading to information disclosure.

Weakness: CWE-201 (Insertion of Sensitive Information Into Sent Data)

## Which versions are affected by CVE-2026-66339?

It affects 2 products.


Products: Gnome Libsoup, Redhat Enterprise Linux.

## How do I fix CVE-2026-66339?

Apply the vendor's patch.

## Is CVE-2026-66339 being exploited?

There is no known exploitation of CVE-2026-66339 in the wild and no public exploit code.

## Other vulnerabilities in Redhat Enterprise Linux

- [CVE-2026-102556](https://insights.sbomify.com/CVE-2026-102556/): Libsoup: libsoup: heap buffer overflow from websocket pong signal type confusion (high 8.6)
- [CVE-2026-102557](https://insights.sbomify.com/CVE-2026-102557/): Libsoup: libsoup: heap buffer overflow during websocket message reassembly (high 8.6)
- [CVE-2026-102558](https://insights.sbomify.com/CVE-2026-102558/): Libsoup: libsoup: heap buffer overflow during websocket receive-buffer growth (high 8.6)
- [CVE-2026-102559](https://insights.sbomify.com/CVE-2026-102559/): Libsoup: libsoup: heap buffer overflow during websocket client-frame masking (high 8.6)
- [CVE-2026-102560](https://insights.sbomify.com/CVE-2026-102560/): Libsoup: libsoup: heap buffer overflow during outgoing permessage-deflate buffer growth (high 8.6)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-66339 and fix it if it is affected.

What it is: CVE-2026-66339 is a medium-severity vulnerability in Redhat Enterprise Linux, published on 24 Jul 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2026-66339 in the wild and no public exploit code.

Affected product: Redhat Enterprise Linux. 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-2026-66339/ (Markdown: https://insights.sbomify.com/CVE-2026-66339/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-66339
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-66339
- OSV: https://osv.dev/vulnerability/CVE-2026-66339

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-66339/
Summaries are generated and may contain mistakes; the official description above is the record.