Apache Tomcat’s DIGEST authenticator is vulnerable to a limited replay attack. An attacker who captures a DIGEST authentication request with a nonce count at the upper boundary of the server’s replay window can replay that request once while the nonce count remains within the window. The replay grants the attacker authenticated access to the requested resource without the victim’s credentials, representing an authentication bypass that can compromise confidentiality and integrity of application data.

Apache Tomcat versions from 11.0.0-M1 to 11.0.24, 10.1.0-M1 to 10.1.57, and 9.0.0-M1 to 9.0.120 are affected. End‑of‑life releases 8.5.0 through 8.5.100 and 7.0.30 through 7.0.109 are also vulnerable, and other unsupported releases may be impacted. The issue is fixed in Apache Tomcat 11.0.25, 10.1.58, and 9.0.121.

The CVSS score of 9.8 classifies this flaw as critical. The EPSS score of less than 1 % indicates a low but nonzero likelihood of exploitation, and the vulnerability is not listed in the CISA KEV catalog. A successful exploit requires an attacker to capture a valid DIGEST authentication exchange before the nonce count reaches its upper limit; after interception, the attacker can replay the request once while the nonce count remains within the replay window. Based on the description, it is inferred that an attacker would need network visibility to the authentication traffic, such as on an unencrypted channel or a compromised network segment, to capture the exchange. Once the replay is performed, the server accepts the request and grants the attacker unauthorized access.