CVE-2025-59045: stalwartlabs stalwart · Unthrottled Resource Allocation
Affects stalwartlabs stalwartSource CVE Database V5
Not known to be exploited · CVSS 7.1 High.
Data as of 26 Oct 2026, 12:55 UTC
- EPSS
- 0.3% chance of exploitation in 30 days – higher than 28% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:NExploitation evidence
Disclosed: evidence found.
CVE published 10 Sep 2025
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors
A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.
What to do
AI-suggested
The primary mitigation is to upgrade Stalwart servers to version 0.13.3 or later, where this vulnerability is fixed. If immediate upgrading is not feasible, organizations should implement strict memory limits at the container or operating system level to prevent a single process from exhausting system memory. Monitoring tools should be configured to alert on unusual memory usage spikes associated with the Stalwart service. Rate limiting CalDAV REPORT requests, especially those involving event expansions, can reduce the risk of abuse. Access controls should be tightened to restrict CalDAV access to trusted and verified users only, minimizing the attack surface. Additionally, auditing calendar event creation for unusually large or suspicious recurring events can help detect potential exploitation attempts. Network segmentation and application-layer firewalls can also be employed to limit exposure of the CalDAV service to internal or trusted networks. Finally, incident response plans should include procedures for quickly identifying and mitigating DoS conditions related to this vulnerability.
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.
References
- github.com/stalwartlabs/stalwart/security/advisories/GHSA-xv4r-q6gr-6pfg (opens in a new tab)
- github.com/stalwartlabs/stalwart/commit/15762fba2ba335e560b8d25f71af085a8b6b6cf2 (opens in a new tab)
- github.com/stalwartlabs/stalwart/blob/main/CHANGELOG.md (opens in a new tab)
- github.com/stalwartlabs/stalwart/releases/tag/v0.13.3 (opens in a new tab)
- tools.ietf.org/html/rfc4791 (opens in a new tab)