CVE-2026-40594
pyLoad has a Session Cookie Security Downgrade via Untrusted X-Forwarded-Proto Header Spoofing (Global State Race Condition)
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.
How to fix CVE-2026-40594
To remediate CVE-2026-40594, upgrade the affected package to a fixed version below.
- —upgrade to 0.5.0b3.dev98 or later
- —upgrade to 0.5.0b3.dev69 or later
Is CVE-2026-40594 being exploited?
Low — EPSS is 0.0%, meaning exploitation activity has not been observed at scale.
Affected packages (2)
- from 0, < 0.5.0b3.dev98
- from 0, < 0.5.0b3.dev69
CVSS scores
| Source | Version | Severity | Vector |
|---|---|---|---|
| osv | CVSS 3.1 | MEDIUM4.8 | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:L |