Vulnerability · Published Apr 21, 2026 · Assigned by GitHub_M
CVE-2026-40594pyLoad: Session Cookie Security Downgrade via Untrusted X-Forwarded-Proto Header Spoofing (Global State Race Condition)
Medium 4.8
In plain English
A medium-severity security flaw in pyload from pyload. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.2% (higher than 7% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official description
pyLoad is a free and open-source download manager written in Python. Prior to 0.5.0b3.dev98, the set_session_cookie_secure before_request 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 SESSION_COOKIE_SECURE on every request. Because pyLoad uses the multi-threaded Cheroot WSGI server (request_queue_size=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. This vulnerability is fixed in 0.5.0b3.dev98.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| PyPI | pyload-ng | 0.5.0b3.dev98 | GHSA-mp82-fmj6-f22v |
| PyPI | pyload-ng | 0.5.0b3.dev69 | PYSEC-2026-125 |
Affected products (as reported)
Weakness: CWE-346 · Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:L
References
- https://github.com/pyload/pyload/security/advisories/GHSA-mp82-fmj6-f22v x_refsource_CONFIRM