CVE-2025-53506
Published: 10 July 2025
Summary
CVE-2025-53506 is a high-severity Uncontrolled Resource Consumption (CWE-400) vulnerability in Apache Tomcat. Its CVSS base score is 7.5 (High).
Operationally, ranked in the top 20.3% of CVEs by exploit likelihood; it is not currently listed in the CISA KEV catalog.
Deeper analysis
CVE-2025-53506 is an uncontrolled resource consumption vulnerability (CWE-400) in Apache Tomcat that occurs when an HTTP/2 client fails to acknowledge the initial settings frame used to reduce the maximum permitted concurrent streams. The flaw affects Tomcat versions 11.0.0-M1 through 11.0.8, 10.1.0-M1 through 10.1.42, and 9.0.0.M1 through 9.0.106, as well as several end-of-life branches including 8.5.0 through 8.5.100. It carries a CVSS 3.1 base score of 7.5 with high availability impact.
An unauthenticated remote attacker can exploit the issue over the network by establishing an HTTP/2 connection and withholding acknowledgment of the SETTINGS frame, causing the server to retain excessive resources and potentially leading to denial of service.
Apache has published fixes in versions 11.0.9, 10.1.43, and 9.0.107; users are advised to upgrade to one of these releases. Corresponding advisories have been issued via the Apache Tomcat mailing list, oss-security, and distributions such as Debian LTS. The associated EPSS score has remained flat at 0.0125 with no material increase since disclosure.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2025-21032
Vulnerability details
Uncontrolled Resource Consumption vulnerability in Apache Tomcat if an HTTP/2 client did not acknowledge the initial settings frame that reduces the maximum permitted concurrent streams. This issue affects Apache Tomcat: from 11.0.0-M1 through 11.0.8, from 10.1.0-M1 through 10.1.42, from 9.0.0.M1…
more
through 9.0.106. The following versions were EOL at the time the CVE was created but are known to be affected: 8.5.0 through 8.5.100. Other EOL versions may also be affected. Users are recommended to upgrade to version 11.0.9, 10.1.43 or 9.0.107, which fix the issue.
- CWE(s)
Related Threats
No named actor attribution yet. ATT&CK technique mapping in progress for this CVE.
Affected Assets
Mitigating Controls
Likely Mitigating Controls AI
Per-CVE control mapping for this CVE has not run yet; the list below is derived from the weakness types (CWEs) cited in the NVD entry.
Limiting concurrent sessions directly prevents uncontrolled resource consumption by capping the number of active sessions per user or account.
Analysis identifies uncontrolled resource consumption indicative of denial-of-service or abuse attempts.
Contingency plan testing includes resource exhaustion scenarios to verify recovery, making it harder for attackers to sustain exploits that cause uncontrolled consumption.
Updated contingency plans include current procedures to detect, contain, and recover from resource exhaustion, limiting an attacker's ability to sustain impact from uncontrolled consumption.
Alternate site allows resumption of operations if resource exhaustion at the primary site is exploited to cause unavailability.
Alternate telecommunications services enable resumption of essential functions when primary services become unavailable due to uncontrolled resource consumption.
The team can analyze and respond to resource exhaustion incidents, reducing the impact of attacks that exploit uncontrolled consumption weaknesses.
Timely maintenance support and spare parts enable rapid recovery from failures induced by uncontrolled resource consumption, shortening the impact window of denial-of-service attacks.