pyLoad has a Session Cookie Security Downgrade via Untrusted X-Forwarded-Proto Header Spoofing (Global State Race Condition)

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

4.8 · CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:L

EPSS

• CVE-2026-40594: 0.17% estimated exploitation activity in the next 30 days; percentile 6.49 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary The setsessioncookiesecure beforerequest handler in src/pyload/webui/app/init.py reads the X-Forwarded-Proto header from any HTTP request without validating that the request originates from a trusted proxy, then mutates the global Flask configuration SESSIONCOOKIESECURE on every request. Because pyLoad uses the multi-threaded Cheroot WSGI server (requestqueuesize=512), this creates a race condition where an attacker's request can influence the Secure flag on other users' session cookies — either downgrading cookie security behind a TLS proxy or causing a session denial-of-service on plain HTTP deployments. Details The vulnerable code is in src/pyload/webui/app/init.py:75-84: The root cause has two components: 1. No origin validation (CWE-346): The X-Forwarded-Proto header is read from any client request. This header is only trustworthy when set by a known reverse proxy. Without ProxyFix middleware or a trusted proxy allowlist, any client can spoof it. The code itself…

Published by the source

16 Apr 2026, 01:20 UTC

Last modified by the source

8 Jun 2026, 20:00 UTC

Source last checked

26 Oct 2026, 13:44 UTC

1. Revision 2 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-mp82-fmj6-f22v

2. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-mp82-fmj6-f22v

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# Patch Next advisory brief: CVE-2026-40594

Advisory: pyLoad has a Session Cookie Security Downgrade via Untrusted X-Forwarded-Proto Header Spoofing (Global State Race Condition)
IDs: CVE-2026-40594, GHSA-mp82-fmj6-f22v
Record: https://patchnext.com/advisories/cve-2026-40594 (revision 2, source checked 26 Oct 2026, 13:44 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 4.8)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: pyload-ng 0.5.0b3.dev98. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI pyload-ng: affected <= 0.5.0b3.dev97; fixed in 0.5.0b3.dev98

## Suggested inspection (read-only)
- `python -m pip show pyload-ng`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on pyload-ng.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-mp82-fmj6-f22v (OSV record GHSA-mp82-fmj6-f22v lists affected ranges: PyPI pyload-ng >=0 <0.5.0b3.dev98 (fixed))
- Verified: https://github.com/advisories/GHSA-mp82-fmj6-f22v (GitHub-reviewed advisory GHSA-mp82-fmj6-f22v lists affected ranges: PyPI pyload-ng >=0 <=0.5.0b3.dev97)

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