CVE-2022-40896 in Utilities Network Management System
Summary
by MITRE • 07/19/2023
A ReDoS issue was discovered in pygments/lexers/smithy.py in pygments through 2.15.0 via SmithyLexer.
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Analysis
by VulDB Data Team • 07/27/2025
The vulnerability CVE-2022-40896 represents a Regular Expression Denial of Service (ReDoS) flaw within the Pygments library's SmithyLexer implementation. This issue affects versions of Pygments up to and including 2.15.0, where the regular expression patterns used for lexing Smithy language syntax contain problematic constructs that can be exploited to cause excessive computational overhead. The SmithyLexer is responsible for parsing Smithy IDL (Interface Definition Language) files, which are used for defining service contracts in AWS services. When processing maliciously crafted Smithy input, the lexer's regular expressions can enter into catastrophic backtracking scenarios, leading to significant performance degradation or complete service unavailability. This vulnerability falls under CWE-400, which specifically addresses Uncontrolled Resource Consumption, and aligns with ATT&CK technique T1499.004 for Network Denial of Service, as the exploitation can result in resource exhaustion that impacts system availability.
The technical implementation of this vulnerability stems from the design of regular expressions within the SmithyLexer class in the pygments/lexers/smithy.py file. The problematic patterns likely contain nested quantifiers or alternation constructs that create exponential backtracking behavior when processing specific input sequences. When an attacker provides input that matches the triggering pattern, the regular expression engine must explore an exponentially growing number of possible matches, causing the CPU utilization to spike dramatically. This behavior occurs because the lexer's regular expressions are not properly bounded in their matching complexity, allowing malicious inputs to force the system into inefficient computational states. The vulnerability manifests during the lexing phase of document processing, where Pygments attempts to tokenize Smithy source code for syntax highlighting or analysis purposes. The impact is particularly severe because Pygments is widely used in development environments, documentation systems, and code analysis tools, making this vulnerability potentially exploitable in multiple contexts.
The operational impact of CVE-2022-40896 extends beyond simple performance degradation to potentially disrupt critical development and deployment workflows. In continuous integration systems, documentation generators, or code review tools that rely on Pygments for syntax highlighting, an attacker could trigger resource exhaustion by submitting malicious Smithy files. This could lead to denial of service conditions that prevent legitimate code analysis, documentation generation, or development activities from completing successfully. The vulnerability is particularly concerning in automated environments where multiple files are processed simultaneously, as the exponential nature of the backtracking can compound the resource consumption. Additionally, since Pygments is integrated into numerous applications and platforms, the potential attack surface is extensive, affecting everything from local development environments to cloud-based code analysis services. Organizations using Pygments in security-sensitive contexts may find their systems vulnerable to this type of resource exhaustion attack, potentially leading to service disruption or even system compromise if the underlying infrastructure is not properly protected against such attacks.
Mitigation strategies for CVE-2022-40896 should focus on immediate version updates and defensive programming practices. The primary recommendation is to upgrade to Pygments version 2.15.1 or later, where the vulnerable regular expressions have been patched or rewritten to eliminate the catastrophic backtracking patterns. Organizations should also implement input validation and sanitization measures when processing user-provided Smithy files, particularly in web applications or services that accept arbitrary code input. This includes setting timeouts on lexing operations and implementing rate limiting to prevent abuse of the parsing functionality. Additionally, security teams should consider implementing monitoring and alerting for unusual CPU utilization patterns that might indicate ReDoS attacks. The fix for this vulnerability demonstrates the importance of proper regular expression design and the need for security reviews of parsing components, particularly those handling untrusted input. Organizations should also consider implementing automated dependency scanning to identify and remediate similar vulnerabilities in their software supply chain, as this type of issue can occur in any library that uses regular expressions for parsing or lexing operations.