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

published 2026-04-16 6 mo ago modified 2026-06-17 4 mo ago also EUVD-2026-24207 , GHSA-mp82-fmj6-f22v , PYSEC-2026-125

cvss: 4.8; version 3.1, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 0.2%; EPSS 0.2% chance of exploitation in 30 days, percentile 6%
public exploits: 0; none known

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.

Patch / fix

fixed in 3

pypi pyload-ng 0.5.0b3.dev69, 0.5.0b3.dev98
pyload-ng_project pyload-ng 0.5.0b3.dev98
pyload pyload 0.5.0b3.dev98

CISA SSVC

Exploitation: Proof of concept is public
Automatable: no
Technical impact: partial
Assessed: 6 mo ago (2026-04-21)

Exploit prediction

0.17% chance of exploitation in the next 30 days, higher than 6% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

github.com https://github.com/pyload/pyload/security/advisories/GHSA-mp82-fmj6-f22v referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by	version	score	vector
CNA	3.1	4.8	CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:L
GitHub	3.1	4.8	CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:L
OSV	3.1	4.8	CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:L

Affected packages

ecosystem	package	affected	fixed in
pypi	pyload-ng	<0.5.0b3.dev98 <0.5.0b3.dev69	0.5.0b3.dev98 0.5.0b3.dev69

Affected products

pyload pyload

Classification

Weakness

CWE-346 Origin Validation Error

References

github.com /pyload/pyload/security/advisories/GHSA-mp82-fmj6-f22v
exploit, web, mitigation, vendor-advisory, evidence
nvd.nist.gov /vuln/detail/CVE-2026-40594
advisory
github.com /pyload/pyload
package
github.com /pypa/advisory-database/tree/main/vulns/pyload-ng/PYSEC-2026-125.yaml
web

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

CPEs and fixed versions use Anchore's correction of NVD's data: Added CPE configurations because not yet analyzed by NVD.

Summary