Stalwart is a mail and collaboration server. Starting in version 0.12.0 and prior to version 0.13.3, a memory exhaustion vulnerability exists in Stalwart's CalDAV implementation that allows authenticated attackers to cause denial-of-service by triggering unbounded memory consumption through recurring event expansion. An authenticated attacker can crash the Stalwart server by creating recurring events with large payloads and triggering their expansion through CalDAV REPORT requests. A single malicious request expanding 300 events with 1000-character descriptions can consume up to 2 GB of memory. The vulnerability exists in the `ArchivedCalendarEventData.expand` function, which processes CalDAV `REPORT` requests with event expansion. When a client requests recurring events in their expanded form using the `<C:expand>` element, the server stores all expanded event instances in memory without enforcing size limits. Users should upgrade to Stalwart version 0.13.3 or later to receive a fix. If immediate upgrading is not possible, implement memory limits at the container/system level; monitor server memory usage for unusual spikes; consider rate limiting CalDAV REPORT requests; and restrict CalDAV access to trusted users only.
Fixes

Solution

No solution given by the vendor.


Workaround

No workaround given by the vendor.

History

Wed, 10 Sep 2025 16:15:00 +0000

Type Values Removed Values Added
Description Stalwart is a mail and collaboration server. Starting in version 0.12.0 and prior to version 0.13.3, a memory exhaustion vulnerability exists in Stalwart's CalDAV implementation that allows authenticated attackers to cause denial-of-service by triggering unbounded memory consumption through recurring event expansion. An authenticated attacker can crash the Stalwart server by creating recurring events with large payloads and triggering their expansion through CalDAV REPORT requests. A single malicious request expanding 300 events with 1000-character descriptions can consume up to 2 GB of memory. The vulnerability exists in the `ArchivedCalendarEventData.expand` function, which processes CalDAV `REPORT` requests with event expansion. When a client requests recurring events in their expanded form using the `<C:expand>` element, the server stores all expanded event instances in memory without enforcing size limits. Users should upgrade to Stalwart version 0.13.3 or later to receive a fix. If immediate upgrading is not possible, implement memory limits at the container/system level; monitor server memory usage for unusual spikes; consider rate limiting CalDAV REPORT requests; and restrict CalDAV access to trusted users only.
Title Stalwart vulnerable to Memory Exhaustion via CalDAV Event Expansion
Weaknesses CWE-770
References
Metrics cvssV4_0

{'score': 7.1, 'vector': 'CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N'}


cve-icon MITRE

Status: PUBLISHED

Assigner: GitHub_M

Published:

Updated: 2025-09-10T16:09:49.485Z

Reserved: 2025-09-08T16:19:26.172Z

Link: CVE-2025-59045

cve-icon Vulnrichment

No data.

cve-icon NVD

Status : Received

Published: 2025-09-10T16:15:41.737

Modified: 2025-09-10T16:15:41.737

Link: CVE-2025-59045

cve-icon Redhat

No data.

cve-icon OpenCVE Enrichment

No data.