CVE-2024-48938 in Znuny
Summary
by MITRE • 10/12/2024
Znuny before LTS 6.5.1 through 6.5.10 and 7.0.1 through 7.0.16 allows DoS/ReDos via email. Parsing the content of emails where HTML code is copied from Microsoft Word could lead to high CPU usage and block the parsing process.
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Analysis
by VulDB Data Team • 06/15/2025
This vulnerability affects Znuny versions prior to LTS 6.5.1 through 6.5.10 and 7.0.1 through 7.0.16, presenting a significant denial of service risk through regular expression denial of service. The flaw manifests when the system processes email content that contains HTML code copied from Microsoft Word documents, creating a scenario where maliciously crafted email payloads can trigger excessive cpu consumption during parsing operations. The vulnerability stems from inadequate input validation and insufficient sanitization of html content within email messages, particularly when dealing with complex microsoft word generated html structures that contain nested tags, styles, and formatting elements. This issue represents a classic reDoS vulnerability where the regular expressions used for parsing html content become exponentially complex when processing malformed or specially crafted input, leading to massive cpu utilization and eventual system unresponsiveness.
The technical implementation of this vulnerability involves the email parsing engine's reliance on regular expressions to extract and process html elements from incoming messages. When html content copied from microsoft word contains certain formatting constructs, malformed tags, or deeply nested structures, the parsing regular expressions can enter into catastrophic backtracking states. This behavior aligns with CWE-400, which categorizes regular expression denial of service vulnerabilities as a fundamental weakness in input handling. The attack vector is particularly insidious because it requires no authentication or specialized privileges, making it accessible to anyone who can send email to the affected system. The operational impact extends beyond simple service disruption as the high cpu usage can cause cascading failures in system resources, potentially affecting other services running on the same infrastructure and leading to extended downtime for critical business operations.
Organizations utilizing affected Znuny versions face substantial operational risks including service interruptions, reduced system availability, and potential business disruption. The vulnerability can be exploited through simple email submission, making it particularly dangerous in environments where email processing is critical for business operations. Attackers can craft emails with carefully constructed html content that will cause the parsing engine to consume excessive computational resources, effectively blocking legitimate email processing and potentially leading to system crashes or resource exhaustion. The issue demonstrates a critical gap in input sanitization and validation within the email processing pipeline, highlighting the need for robust defenses against malformed content. This vulnerability directly relates to ATT&CK technique T1499.004 which covers network denial of service attacks through resource exhaustion, and also connects to ATT&CK technique T1566.001 which involves social engineering through email delivery mechanisms.
Mitigation strategies should focus on immediate patching of affected Znuny versions to LTS 6.5.11 and 7.0.17 respectively, which contain fixes for the regular expression parsing issues. Organizations should implement additional input validation measures including html sanitization, content length limits, and timeout mechanisms for email processing operations. Network-level protections such as rate limiting for email submissions and monitoring for unusual cpu utilization patterns can provide additional defensive layers. The implementation of automated email scanning and filtering systems can help identify and quarantine potentially malicious content before it reaches the parsing engine. System administrators should also consider implementing resource monitoring and alerting for cpu utilization spikes during email processing, enabling rapid response to potential exploitation attempts. The fix addresses the core issue by optimizing regular expression patterns and implementing more efficient html parsing algorithms that can handle complex content without entering catastrophic backtracking states, thereby preventing the resource exhaustion that leads to system unresponsiveness.