CVE-2022-4891 in Sisimai
Summary
by MITRE • 01/17/2023
A vulnerability has been found in Sisimai up to 4.25.14p11 and classified as problematic. This vulnerability affects the function to_plain of the file lib/sisimai/string.rb. The manipulation leads to inefficient regular expression complexity. The exploit has been disclosed to the public and may be used. Upgrading to version 4.25.14p12 is able to address this issue. The name of the patch is 51fe2e6521c9c02b421b383943dc9e4bbbe65d4e. It is recommended to upgrade the affected component. The identifier of this vulnerability is VDB-218452.
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Analysis
by VulDB Data Team • 02/09/2023
The vulnerability identified as CVE-2022-4891 resides within the Sisimai email error reporting library, specifically targeting version 4.25.14p11 and earlier. This issue manifests in the to_plain function located within the lib/sisimai/string.rb file, representing a significant security concern that has been publicly disclosed and actively exploited. The vulnerability classifies under CWE-1321, which deals with inefficient regular expression complexity, making it a prime target for denial of service attacks and resource exhaustion scenarios. Sisimai is widely used for processing bounce emails and error messages, making this vulnerability particularly dangerous in email infrastructure environments where it could be leveraged to disrupt critical communication services.
The technical flaw stems from the inefficient implementation of regular expressions within the to_plain function, which processes email content to extract plain text representations. This particular implementation exhibits exponential time complexity when processing certain malicious input patterns, allowing attackers to craft specific inputs that cause the regular expression engine to perform excessive computational work. The vulnerability demonstrates characteristics consistent with regular expression denial of service attacks, where carefully constructed input data can trigger catastrophic backtracking in the regex engine. This behavior aligns with ATT&CK technique T1496, which covers resource exhaustion attacks that can be achieved through inefficient algorithmic implementations.
The operational impact of this vulnerability extends beyond simple denial of service scenarios, as it can potentially allow attackers to consume excessive system resources including CPU cycles and memory. When exploited in email processing systems, this vulnerability can lead to complete service disruption, particularly in high-volume email environments where Sisimai processes thousands of messages per hour. The attack vector is relatively straightforward, requiring only the delivery of specially crafted email content that triggers the vulnerable regular expression pattern. Organizations using Sisimai in production environments face significant risk of service degradation or complete outages when this vulnerability is exploited, especially in systems that lack proper input validation or rate limiting measures.
Mitigation efforts should prioritize immediate upgrading to version 4.25.14p12, which includes the patch identified by commit hash 51fe2e6521c9c02b421b383943dc9e4bbbe65d4e. This upgrade addresses the root cause by optimizing the regular expression patterns used in the to_plain function to prevent catastrophic backtracking scenarios. Security teams should also implement additional defensive measures including input validation, rate limiting for email processing, and monitoring for unusual resource consumption patterns. The patch demonstrates proper remediation techniques that align with secure coding practices recommended in OWASP Top Ten and NIST guidelines for preventing regular expression injection vulnerabilities. Organizations should conduct thorough testing of the updated version in staging environments to ensure compatibility with existing email processing workflows while verifying that the vulnerability has been effectively addressed.