CVE-2026-62641 in Roundcube
Summary
by MITRE • 07/14/2026
In Roundcube Webmail before 1.6.17 and 1.7.x before 1.7.2, the TNEF decoder was subject to denial of service via a crafted compressed-RTF size.
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Analysis
by VulDB Data Team • 07/14/2026
The vulnerability in Roundcube Webmail affects versions prior to 1.6.17 and 1.7.x prior to 1.7.2, specifically within the TNEF (Transport Neutral Encapsulation Format) decoder component. This flaw represents a denial of service condition that can be triggered by crafting maliciously formatted TNEF attachments containing compressed RTF data with manipulated size parameters. The TNEF format is commonly used in Microsoft Outlook environments to encapsulate rich text formatting and embedded objects within email messages, making it a legitimate feature that must be supported for interoperability.
The technical implementation flaw occurs when the TNEF decoder processes compressed RTF content where the reported size of the compressed data does not match the actual decompressed size or when the compression parameters are manipulated to cause excessive memory allocation during decompression. This type of vulnerability falls under CWE-400, which covers resource exhaustion conditions that can lead to denial of service attacks. The decoder fails to properly validate the compression metadata and size indicators before attempting to allocate memory resources for decompression operations.
The operational impact of this vulnerability is significant as it allows remote attackers to consume excessive system resources or cause application crashes by sending specially crafted TNEF attachments. When a vulnerable Roundcube instance processes such malicious emails, the TNEF decoder may enter infinite loops, allocate excessive memory, or trigger stack overflows depending on how the compression parameters are manipulated. This can result in complete service unavailability for users attempting to access their email accounts, effectively rendering the webmail service unusable until the affected process is restarted.
Security practitioners should implement immediate mitigations including updating to Roundcube versions 1.6.17 or 1.7.2 and later, which contain patches addressing the TNEF decoder validation issues. Organizations may also consider implementing email filtering rules that block TNEF attachments entirely if they are not required for business operations, though this approach reduces functionality. The vulnerability demonstrates the importance of proper input validation in legacy code components and highlights how seemingly benign features like TNEF support can become attack vectors when not properly secured against malformed data inputs.
From an adversarial perspective, this vulnerability aligns with ATT&CK technique T1499.004 which covers network denial of service attacks through resource exhaustion. Attackers could leverage this weakness to perform sustained DoS attacks against email servers or individual user accounts, potentially causing significant disruption to business communications and requiring system administrators to spend considerable time troubleshooting and implementing fixes.
The root cause analysis reveals that the vulnerability stems from inadequate bounds checking in the TNEF decompression routine where size parameters are trusted without validation before memory allocation occurs. This pattern of trust-based processing is common in legacy software where security considerations were not fully integrated into the original design phases. Proper defense-in-depth strategies should include implementing strict limits on decompression operations, adding comprehensive input sanitization for all external data, and conducting regular security audits of third-party components that handle complex binary formats.
Organizations should also consider implementing monitoring solutions that can detect unusual resource consumption patterns or repeated processing of suspicious email attachments, as these behaviors often precede successful exploitation attempts. The patching process requires careful testing to ensure that legitimate TNEF processing continues to function correctly while eliminating the vulnerability conditions that allow malicious inputs to cause system instability.