CVE-2026-77762 is a race condition in Apache Tomcat that can inject trailer fields into another HTTP/2 request. Apache rates it Low in its Tomcat 11 advisory. Upgrade to the fixed release for your Tomcat branch: 11.0.26, 10.1.60, or 9.0.122. Although this article places the flaw in the broader HTTP/2 request-mix-up family, that family label is not the precise description of this CVE.
What CVE-2026-77762 does
Apache’s Tomcat 11 security advisory describes the issue this way: “A race condition allowed an attacker to inject trailer fields into another HTTP/2 request.” The flaw concerns trailer fields crossing between HTTP/2 requests under concurrent execution.
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The documented impact is specifically trailer-field injection. The advisory does not establish general disclosure of request data or describe a particular downstream application effect. It also does not provide a workaround, exploit prerequisites, a CVSS score, or evidence of exploitation in the wild.
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The CVE Program record lists these affected ranges. It also notes that unsupported versions beyond the listed ranges may be affected.
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| Tomcat branch | Affected versions listed | Fixed release |
|---|---|---|
| 11 | 11.0.0-M1 through 11.0.25 | 11.0.26 |
| 10.1 | 10.1.0-M1 through 10.1.59 | 10.1.60 |
| 9 | 9.0.39 through 9.0.121 | 9.0.122 |
| 8.5 | 8.5.59 through 8.5.100 (known affected; branch was end-of-life when the CVE was created) | Not stated; this branch was end-of-life |
These ranges and recommendations are from the CVE Program record. Apache’s branch advisories identify the corresponding fix commits: Tomcat 11 (fd309997), Tomcat 10.1 (77d2d593), and Tomcat 9 (71f27c2e). For operators, use the named fixed release rather than treating a commit hash as a deployment instruction.
How to check and remediate
- Identify the Tomcat version actually running in each environment, including production, test, and any separately maintained instances.
- Compare that version with the affected range for its branch. If it falls within a listed range, plan an upgrade to the corresponding fixed release.
- Upgrade to Tomcat 11.0.26, 10.1.60, or 9.0.122, as applicable, and verify that the deployed instance reports the intended version.
- If you run Tomcat 8.5.59–8.5.100, treat it as known affected and account for the branch’s end-of-life status; the CVE record names no fixed 8.5 release.
- If your release is unsupported or outside the ranges shown, do not assume it is unaffected: the CVE Program record cautions that other unsupported versions may also be affected.
How this differs from other Tomcat HTTP/2 mix-up issues
“Request mix-up” is a family-level label for distinct HTTP/2 vulnerabilities, not a mechanism unique to CVE-2026-77762. In particular, CVE-2026-86350 is a separate request-header mix-up issue. Apache attributes it to inconsistent interpretation of HTTP/2 requests caused by a regression in the fix for CVE-2026-41293. The Tomcat 11 advisory lists it for versions 11.0.22 to 11.0.25, while the Tomcat 9 advisory lists it for 9.0.118 to 9.0.121. Those details and ranges must not be applied to CVE-2026-77762.
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Apache’s advisories also discuss older, separate HTTP/2 mix-up vulnerabilities, including CVE-2020-17527 and CVE-2020-13943. Their existence explains the family terminology; it does not make their mechanisms or fixes interchangeable with this CVE.
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Apache’s advisories state that the issue was reported to the Tomcat security team on 21 August 2026 and made public on 23 September 2026. The Tomcat 11 advisory rates CVE-2026-77762 Low. The reviewed advisories do not establish a broader confidentiality impact, a workaround, or known in-the-wild exploitation, so those should not be inferred from the trailer-injection description alone.
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