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CVE-2026-77762 is a race condition in Apache Tomcat that can inject HTTP/2 trailer fields from one request into another. Apache recommends upgrading to Tomcat 11.0.26, 10.1.60, or 9.0.122, depending on your release branch. The phrase “HTTP/2 request-mixup family” is a broad label: this CVE is specifically about trailer-field injection, not the separate request-header mix-up tracked as CVE-2026-86350.
What CVE-2026-77762 does
Apache Tomcat describes CVE-2026-77762 as a concurrent-execution race condition affecting HTTP/2. In Apache’s words, “A race condition allowed an attacker to inject trailer fields into another HTTP/2 request.” The Tomcat 11 advisory rates the issue Low.
The published description establishes trailer-field injection across requests. It does not establish general disclosure of request data or a specific effect on applications using Tomcat; those broader outcomes should not be inferred from the advisory.
Which Tomcat versions are affected?
The CVE Program record lists these affected version ranges. Check the exact branch and version you deploy, rather than relying on “Tomcat” alone.
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| Tomcat branch | Affected versions listed | Recommended 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 are identified as known affected versions; this line was already end-of-life when the CVE was created | Not stated for this end-of-life line; migrate to a supported release line and apply its fixed release |
The CVE record cautions that other unsupported versions may also be affected. If you run a version outside the listed ranges—especially an unsupported one—do not treat that absence as proof that it is safe.
How to remediate
- Identify the deployed branch and version. Check the Tomcat version running in each environment, including production, test, and any separately managed instances.
- Upgrade to the corresponding fixed release. Use Tomcat 11.0.26 for the 11.x branch, 10.1.60 for 10.1.x, or 9.0.122 for 9.0.x, as recommended by the CVE Program record.
- Verify the running version after deployment. Confirm that the service is actually running the upgraded release; changing a package or image does not by itself establish that every instance has been updated.
Apache’s branch advisories identify fix commits fd309997 for 11.x, 77d2d593 for 10.1.x, and 71f27c2e for 9.0.x. These are useful for tracing the fixes in source, but the recommended release versions are the direct upgrade targets for operators.
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How this differs from CVE-2026-86350
CVE-2026-86350 is a separate HTTP/2 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. Its mechanism and affected ranges should not be substituted for those of CVE-2026-77762.
| Issue | Documented mechanism | Version detail in Apache advisories |
|---|---|---|
| CVE-2026-77762 | Race condition permits trailer fields to be injected into another HTTP/2 request | See the cross-branch ranges and fixed releases above |
| CVE-2026-86350 | Request-header mix-up associated with inconsistent interpretation after a regression in the CVE-2026-41293 fix | Tomcat 11 advisory: 11.0.22 to 11.0.25; Tomcat 9 advisory: 9.0.118 to 9.0.121 |
Apache advisories also document older, distinct HTTP/2 mix-up vulnerabilities, including CVE-2020-17527 and CVE-2020-13943. “Request mix-up” is therefore a useful family-level description, not a single mechanism shared by every CVE.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What the public advisories do not establish
The reviewed CVE and Apache advisory material does not establish a workaround, exploit prerequisites, known exploitation in the wild, a CVSS score, or a confirmed broader confidentiality impact. For CVE-2026-77762, the supported impact statement remains the documented possibility of trailer-field injection into another HTTP/2 request.
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Sources
- CVE Program record for CVE-2026-77762
- Apache Tomcat 11 security advisories
- Apache Tomcat 10.1 security advisories
- Apache Tomcat 9 security advisories
- Apache oss-security notice
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