Security Digest · Vulnerability record
CVE-2026-65927: Apache Tomcat: RewriteValve [N] restarts at the second rule and may bypass access control
Off-by-one Error vulnerability in Apache Tomcat impacting the [N] flag on the rewrite valves causes rewrite processing to restart at the second rule rather than the first rule.
CVSS 7.5 High EPSS 0.7% · p52 Patch this week
Should you act?
Normal patch cycle
No exploitation signal; fix it in your next routine update if you are affected. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.
- No confirmed exploitation. It is not in CISA’s KEV catalog and CISA’s SSVC assessment records no known exploitation. That can change quickly after a public write-up; re-check if you are affected.
- EPSS 0.7%, percentile 52: FIRST’s model estimates a 0.7% chance of exploitation activity in the next 30 days, higher than 52% of all scored CVEs (moderate). EPSS is a probability, not a verdict.
- Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
- Editorial verdict: Patch this week. Apache Tomcat August 2026: Security Constraint Bypasses — Upgrade Tomcat, including the copy embedded in Spring Boot apps, this week; the access-control bypasses matter wherever you rely on web.xml security constraints or container authentication, and none is known to be exploited.
What it is
Off-by-one Error vulnerability in Apache Tomcat impacting the [N] flag on the rewrite valves causes rewrite processing to restart at the second rule rather than the first rule. This issue affects Apache Tomcat: from 11.0.0-M1 through 11.0.24, from 10.1.0-M1 through 10.1.57, from 9.0.0.M1 through 9.0.120. The following versions were EOL at the time the CVE was created but are known to be affected: from 8.5.0 through 8.5.100. Other unsupported versions may also be affected. Users are recommended to upgrade to version 11.0.25, 10.1.58 or 9.0.121 which fix the issue.
Weakness type: CWE-193.
Product: Apache Software Foundation Apache Tomcat · Assigned by: apache · Published: 2026-08-25
Affected and fixed versions
| Vendor | Product | Affected versions (per CVE record) |
|---|---|---|
| Apache Software Foundation | Apache Tomcat | 11.0.0-M1 <= 11.0.24, 10.1.0-M1 <= 10.1.57, 9.0.0.M1 <= 9.0.120, 8.5.0 <= 8.5.100 |
Severity scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| CISA-ADP | 3.1 | 7.5 High | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H |
- Attack vector: network (remotely reachable)
- Attack complexity: low
- Privileges required: none (no login)
- User interaction: none
- Scope: unchanged
CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.
Exploitation and urgency
- CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
- CISA SSVC assessment: exploitation none, automatable yes, technical impact partial.
- FIRST EPSS (model of 2026-10-21): 0.68% probability of exploitation activity in the next 30 days; percentile 52.
Timeline
- — CVE record published by apache
- — erroneo.us brief: Apache Tomcat August 2026: Security Constraint Bypasses
- — CVE record last updated
Sources and references
Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.
Vendor and project advisories, patches
- lists.apache.org lists.apache.org
Vulnerability records
- CVE.org record CVE-2026-65927 cve.org
- NVD entry CVE-2026-65927 nvd.nist.gov
Other references from the CVE record and advisory
- openwall.com openwall.com