CVE-2026-40071: pyLoad Privilege Escalation Vulnerability

CVE-2026-40071 Overview

CVE-2026-40071 is a Broken Access Control vulnerability affecting pyLoad, a free and open-source download manager written in Python. The vulnerability exists in several WebUI JSON endpoints that enforce weaker permissions than the core API methods they invoke, allowing authenticated low-privileged users to perform unauthorized MODIFY operations.

Critical Impact

Authenticated users with limited privileges can bypass pyLoad's permission model to execute unauthorized modification operations through the /json/package_order, /json/link_order, and /json/abort_link endpoints.

Affected Products

• pyLoad versions prior to 0.5.0b3.dev97

Discovery Timeline

• April 09, 2026 - CVE-2026-40071 published to NVD
• April 09, 2026 - Last updated in NVD database

Technical Details for CVE-2026-40071

Vulnerability Analysis

This vulnerability stems from an inconsistency between the permission checks implemented at the WebUI JSON endpoint layer versus the core API permission model. The affected endpoints—/json/package_order, /json/link_order, and /json/abort_link—fail to properly validate user permissions before invoking underlying API methods that require elevated privileges. This creates a privilege escalation vector where authenticated users with restricted access can perform MODIFY operations that should be denied according to pyLoad's internal permission model.

The weakness is classified under CWE-863 (Incorrect Authorization), indicating that the software performs authorization checks improperly, allowing attackers to access resources or perform actions beyond their intended permission level.

Root Cause

The root cause is an improper access control implementation where the WebUI JSON layer does not synchronize its permission enforcement with the stricter permission requirements of the core API methods. When processing requests to the vulnerable endpoints, the WebUI validates permissions using a less restrictive model, then passes the request to core API functions that would normally reject such operations from low-privileged users.

Attack Vector

An attacker who has obtained valid low-privileged credentials to a pyLoad instance can exploit this vulnerability over the network. The attack requires:

1. Authentication to the pyLoad WebUI with any valid user account
2. Sending crafted requests to the vulnerable JSON endpoints (/json/package_order, /json/link_order, or /json/abort_link)
3. The WebUI accepts the request and invokes the underlying API method with elevated privileges

The exploitation does not require user interaction and can be performed remotely. The vulnerability allows manipulation of package ordering, link ordering, and the ability to abort links—operations that should be restricted to users with MODIFY permissions.

Detection Methods for CVE-2026-40071

Indicators of Compromise

• Unexpected modifications to download package ordering by users without MODIFY permissions
• Log entries showing low-privileged user accounts accessing /json/package_order, /json/link_order, or /json/abort_link endpoints
• Audit trail anomalies where link abort operations are performed by restricted accounts

Detection Strategies

• Monitor pyLoad access logs for requests to the vulnerable JSON endpoints from accounts that should not have MODIFY permissions
• Implement application-layer monitoring to detect permission bypass patterns in API calls
• Review user activity logs for authorization inconsistencies between WebUI actions and expected permission levels

Monitoring Recommendations

• Configure alerting for any access to sensitive JSON endpoints by accounts with restricted permission levels
• Enable verbose logging in pyLoad to capture detailed request information for forensic analysis
• Deploy web application firewall (WAF) rules to monitor and log access patterns to the vulnerable endpoints

How to Mitigate CVE-2026-40071

Immediate Actions Required

• Upgrade pyLoad to version 0.5.0b3.dev97 or later immediately
• Review user accounts and ensure proper permission levels are assigned
• Audit recent activity logs for potential exploitation attempts on the vulnerable endpoints
• Consider temporarily restricting access to the pyLoad WebUI until patching is complete

Patch Information

The vulnerability has been fixed in pyLoad version 0.5.0b3.dev97. The fix ensures that the WebUI JSON endpoints properly enforce the same permission checks as the core API methods they invoke. For detailed information about the security fix, refer to the GitHub Security Advisory.

Workarounds

• Restrict network access to the pyLoad WebUI to trusted IP addresses only until patching is complete
• Disable or remove low-privileged user accounts that do not require WebUI access
• Implement reverse proxy authentication to add an additional layer of access control
• Monitor and log all requests to the vulnerable endpoints as a temporary detection measure