Executive brief
Roundcube Webmail, a widely used browser-based email client, is vulnerable to a denial-of-service attack. An attacker can send a specially crafted email with a TNEF (winmail.dat) attachment that, when opened by a user, causes the mail server to enter an infinite loop. This can lead to service instability or unavailability for the affected user or the entire webmail instance.
Technical details
A vulnerability classified as CWE-835 (Loop with Unreachable Exit Condition) exists in the TNEF (winmail.dat) decoder of Roundcube Webmail. The flaw is located in the rcube_tnef_decoder.php component. An unauthenticated remote attacker can exploit this by sending an email containing a malformed TNEF attachment. When a user attempts to view the email, the decoder enters an infinite loop, consuming system resources and resulting in a Denial of Service (DoS). The issue is addressed in versions 1.6.17 and 1.7.2.
Affected products
- Roundcube Webmail before 1.6.17, 1.7.x before 1.7.2
Timeline
- 2026-07-05: patched: Security updates 1.6.17 and 1.7.2 released by vendor.
- 2026-07-14: advisory: CVE published to NVD.
References
- https://github.com/roundcube/roundcubemail/commit/132ac8dd5a55c8466be12de1daf84355697ffa89
- https://github.com/roundcube/roundcubemail/commit/877269c79359d959a94f13c9070cab0f3389c193
- https://github.com/roundcube/roundcubemail/commit/a007321346380136b3de2bd75b486b04f63c0d38
- https://github.com/roundcube/roundcubemail/commit/fb952956c6eaf29e963f1a718d028d66e7957ce0
- https://github.com/roundcube/roundcubemail/releases/tag/1.6.17
- https://github.com/roundcube/roundcubemail/releases/tag/1.7.2
- https://roundcube.net/news/2026/07/05/security-updates-1.6.17-and-1.7.2