Description
A flaw was found in the ChunkReader component of the Undertow web server, which is used to handle chunked transfer encoding in HTTP requests. The issue occurs because a security check for the chunk size is performed before the value is shifted, allowing a specifically crafted 15-digit chunk size to bypass the limit and overflow into internal state flags. This can cause the server to terminate a request body prematurely and interpret the remaining data as a separate, smuggled request.
Affected products
| Vendor | Product | Affected | Fixed |
|---|---|---|---|
| Red Hat | Red Hat build of Apache Camel for Spring Boot 4 | — | — |
| Red Hat | Red Hat Enterprise Linux 8 | — | — |
| Red Hat | Red Hat Enterprise Linux 9 | — | — |
| Red Hat | Red Hat Fuse 7 | — | — |
| Red Hat | Red Hat JBoss Enterprise Application Platform 7 | — | — |
| Red Hat | Red Hat JBoss Enterprise Application Platform 8 | — | — |
| Red Hat | Red Hat JBoss Enterprise Application Platform Expansion Pack | — | — |
| Red Hat | Red Hat Single Sign-On 7 | — | — |
Fixed in Linux distributions
Distributions backport fixes, so the version that fixes this vulnerability differs per release — upgrade to at least the version shown. From the distributions' security trackers and advisories.
Debian
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian 14 | undertow | No fix yet | — |
Ubuntu
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu 26.10 | undertow | No fix yet | — |
| Ubuntu 26.04 LTS | undertow | No fix yet | — |
Show 5 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu Pro 24.04 LTS | undertow | No fix yet | — |
| Ubuntu Pro 22.04 LTS | undertow | No fix yet | — |
| Ubuntu Pro 20.04 LTS | undertow | No fix yet | — |
| Ubuntu Pro 18.04 LTS | undertow | No fix yet | — |
| Ubuntu Pro 16.04 LTS | undertow | No fix yet | — |
References
- https://access.redhat.com/security/cve/CVE-2026-91920 vdb-entry
- RHBZ#2528758 issue-tracking