CVE-2021-41250 in Python Discord Bot
Summary
by MITRE • 11/06/2021
Python discord bot is the community bot for the Python Discord community. In affected versions when a non-blacklisted URL and an otherwise triggering filter token is included in the same message the token filter does not trigger. This means that by including any non-blacklisted URL moderation filters can be bypassed. This issue has been resolved in commit 67390298852513d13e0213870e50fb3cff1424e0
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Analysis
by VulDB Data Team • 11/10/2021
The vulnerability described in CVE-2021-41250 affects a Python Discord community bot that serves as a moderation tool for the Python Discord server. This bot implements token filtering mechanisms to detect and prevent the posting of sensitive information including API keys, tokens, and other confidential data. The flaw exists in the bot's message processing logic where it fails to properly evaluate filter conditions when both non-blacklisted URLs and trigger tokens appear within the same message. This represents a critical security weakness in automated moderation systems that rely on pattern matching to identify potentially harmful content.
The technical implementation flaw stems from improper logical evaluation within the bot's filtering system. When a message contains both a non-blacklisted URL and a filter-triggering token, the bot's conditional logic incorrectly processes these elements in a way that allows the token filter to be bypassed entirely. This occurs because the URL validation mechanism takes precedence over the token detection logic, creating a scenario where legitimate security alerts are not raised even when sensitive information is present in messages that also contain seemingly benign web addresses. The vulnerability specifically affects the order of operations in the bot's message processing pipeline, where URL validation occurs before or alongside token detection, preventing proper enforcement of security policies.
The operational impact of this vulnerability is significant for any community or organization using similar automated moderation systems. Attackers can exploit this weakness by crafting messages that contain both legitimate URLs and sensitive tokens, effectively evading detection by security filters. This bypass mechanism undermines the integrity of automated content moderation systems and could allow malicious actors to post confidential information without triggering alerts. The vulnerability particularly affects platforms where community members can post content that may contain both publicly accessible links and private credentials, creating a window of opportunity for information leakage. Organizations relying on such systems for security monitoring may experience false negatives in their automated detection capabilities, leading to potential security incidents going unnoticed.
The fix for this vulnerability was implemented through a specific code commit that addresses the logical flow in the token filtering system. The resolution involves modifying the conditional evaluation order to ensure that token detection occurs independently of URL validation, preventing the bypass scenario. This change aligns with security best practices for filter implementation and follows principles outlined in CWE-1004 which addresses weaknesses in security-relevant code. Organizations should implement similar fixes in their own automated moderation systems, ensuring that different types of security checks are evaluated independently rather than allowing one detection mechanism to override another. The mitigation approach also aligns with ATT&CK technique T1566 which covers social engineering methods that bypass security controls, as this vulnerability represents a bypass of automated security measures through clever message construction.
Security teams should conduct thorough reviews of their own token filtering and content moderation systems to identify similar logical flaws where one type of detection can interfere with another. This vulnerability demonstrates the importance of proper input validation and the need for comprehensive testing of security controls under various conditions. The fix serves as a reminder that even seemingly simple security mechanisms can contain complex logical flaws that create exploitable bypass paths. Organizations should implement regular security testing of their automated systems, particularly focusing on edge cases where multiple detection mechanisms interact with each other to ensure that security controls remain effective against sophisticated attack patterns.