CVE-2025-59045 Stalwart vulnerable to Memory Exhaustion via CalDAV Event Expansion
Authenticated attackers can crash the Stalwart mail server by triggering unbounded memory consumption via CalDAV recurring event expansion.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2025-59045?
CVE-2025-59045 is a high-severity denial of service vulnerability in stalwartlabs stalwart, published on 10 Sep 2025. Any signed-in user can exploit it over the network, with no action from the victim.
Official 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.
Weakness: CWE-770
Which versions are affected by CVE-2025-59045?
How do I fix CVE-2025-59045?
No fix has been published for CVE-2025-59045 yet. Limit exposure of the affected software until one is available.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2025-59045 being exploited?
There is no known exploitation of CVE-2025-59045 in the wild and no public exploit code.
Sources
Also known as GHSA-xv4r-q6gr-6pfg.