Chunk size overflow in Undertow web server enables request smuggling
Key facts
- Attack vector
- Network
- Privileges required
- None
- User interaction
- None
- Attack complexity
- Low
- Impact type
- —
- Confidentiality · integrity · availability
- None · Low · Low
- Fix status
- No fix listed
Attack profile from CVSS 3.1 · CNA. Fix status from CNA and Red Hat.
Summary
Undertow web server, which handles chunked HTTP transfer encoding, checks the chunk size before shifting its value. A crafted 15-digit chunk size bypasses that limit and overflows into internal state flags, so the server can end a request body early and treat the remaining data as a smuggled request (CWE-444). An unauthenticated remote attacker can trigger this over the network with low complexity, affecting integrity and availability.
Written with Claude Haiku 5.5 from the sources below · 2026-11-03
Description from the CNA
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.
Why it matters now
SSVC decision points
CISA ADP · SSVC 2.0.3
- Exploitation
- None
- Automatable
- Yes
- Technical impact
- Partial
The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.
Affected products
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| Red Hat | Red Hat build of Apache Camel for Spring Boot 4 | — | — | No fix listed | CNA |
| Red Hat | Red Hat Enterprise Linux 8 | — | — | No fix listed | CNA |
| Red Hat | Red Hat Enterprise Linux 8 | — | — | No fix listed | CNA |
| Red Hat | Red Hat Enterprise Linux 9 | — | — | No fix listed | CNA |
| Red Hat | Red Hat Fuse 7 | — | — | Not affected | CNA |
| Red Hat | Red Hat JBoss Enterprise Application Platform 7 | — | — | No fix listed | CNA |
| Red Hat | Red Hat JBoss Enterprise Application Platform 7 | — | — | No fix listed | CNA |
| Red Hat | Red Hat JBoss Enterprise Application Platform 7 | — | — | No fix listed | CNA |
| Red Hat | Red Hat JBoss Enterprise Application Platform 7 | — | — | No fix listed | CNA |
| Red Hat | Red Hat JBoss Enterprise Application Platform 8 | — | — | No fix listed | CNA |
| Red Hat | Red Hat JBoss Enterprise Application Platform Expansion Pack | — | — | Not affected | CNA |
| Red Hat | Red Hat Single Sign-On 7 | — | — | No fix listed | CNA |
- Red Hat build of Apache Camel for Spring Boot 4 VendorRed Hat Affected — Fixed in — No fix listed CNA
- Red Hat Enterprise Linux 8 VendorRed Hat Affected — Fixed in — No fix listed CNA
- Red Hat Enterprise Linux 8 VendorRed Hat Affected — Fixed in — No fix listed CNA
- Red Hat Enterprise Linux 9 VendorRed Hat Affected — Fixed in — No fix listed CNA
- Red Hat Fuse 7 VendorRed Hat Affected — Fixed in — Not affected CNA
- Red Hat JBoss Enterprise Application Platform 7 VendorRed Hat Affected — Fixed in — No fix listed CNA
- Red Hat JBoss Enterprise Application Platform 7 VendorRed Hat Affected — Fixed in — No fix listed CNA
- Red Hat JBoss Enterprise Application Platform 7 VendorRed Hat Affected — Fixed in — No fix listed CNA
- Red Hat JBoss Enterprise Application Platform 7 VendorRed Hat Affected — Fixed in — No fix listed CNA
- Red Hat JBoss Enterprise Application Platform 8 VendorRed Hat Affected — Fixed in — No fix listed CNA
- Red Hat JBoss Enterprise Application Platform Expansion Pack VendorRed Hat Affected — Fixed in — Not affected CNA
- Red Hat Single Sign-On 7 VendorRed Hat Affected — Fixed in — No fix listed CNA
CPE names CNA · 8
| CPE | Versions | Role | Vendor |
|---|---|---|---|
| cpe:/a:redhat:camel_spring_boot:4 | 4 | — | Red Hat |
| cpe:/a:redhat:enterprise_linux:8 | 8 | — | Red Hat |
| cpe:/a:redhat:enterprise_linux:9 | 9 | — | Red Hat |
| cpe:/a:redhat:jboss_fuse:7 | 7 | — | Red Hat |
| cpe:/a:redhat:jboss_enterprise_application_platform:7 | 7 | — | Red Hat |
| cpe:/a:redhat:jboss_enterprise_application_platform:8 | 8 | — | Red Hat |
| cpe:/a:redhat:jbosseapxp | — | — | Red Hat |
| cpe:/a:redhat:red_hat_single_sign_on:7 | 7 | — | Red Hat |
- cpe:/a:redhat:camel_spring_boot:4 Versions 4 — ·Red Hat
- cpe:/a:redhat:enterprise_linux:8 Versions 8 — ·Red Hat
- cpe:/a:redhat:enterprise_linux:9 Versions 9 — ·Red Hat
- cpe:/a:redhat:jboss_fuse:7 Versions 7 — ·Red Hat
- cpe:/a:redhat:jboss_enterprise_application_platform:7 Versions 7 — ·Red Hat
- cpe:/a:redhat:jboss_enterprise_application_platform:8 Versions 8 — ·Red Hat
- cpe:/a:redhat:jbosseapxp Versions — — ·Red Hat
- cpe:/a:redhat:red_hat_single_sign_on:7 Versions 7 — ·Red Hat
Remediation
The sources list no fixed version for Red Hat build of Apache Camel for Spring Boot 4, Red Hat Enterprise Linux 8, Red Hat Enterprise Linux 9, Red Hat JBoss Enterprise Application Platform 7, Red Hat JBoss Enterprise Application Platform 8 and Red Hat Single Sign-On 7. Red Hat states that no fix is planned for JBoss Enterprise Application Platform 7 and that none is available for the other listed products, while Red Hat Fuse 7 and the JBoss Enterprise Application Platform Expansion Pack are not affected.
Written with Claude Haiku 5.5 from the sources below · 2026-11-03
Vendor assessments
Red Hat
Red Hat rating: Moderate. Red Hat's page for this CVE →
| Product | Status | Plan or fix |
|---|---|---|
| Red Hat Enterprise Linux 8 | Affected | — |
| Red Hat Enterprise Linux 9 | Affected | — |
| Red Hat JBoss Enterprise Application Platform 7 | Affected | No fix planned: Will not fix |
| Red Hat JBoss Enterprise Application Platform 8 | Affected | No fix yet |
| Red Hat Single Sign-On 7 | Affected | No fix yet |
| Red Hat build of Apache Camel for Spring Boot 4 | Affected | No fix yet |
Not affected: 2 products
- Red Hat Fuse 7
- Red Hat JBoss Enterprise Application Platform Expansion Pack
Timeline
- 2026-10-30 Threatist record created from CVE-2026-91920
- 2026-10-30 Alias added: GHSA-3f65-g3hr-c59r
- 2026-10-30 Affected versions changed · Red Hat
- 2026-10-31 Priority changed: MEDIUM → LOW
- 2026-11-02 CISA SSVC decision points changed
- 2026-11-03 Affected versions changed · CNA
- 2026-11-03 Affected versions changed · Red Hat
References
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Sources
- CVE-2026-91920 · CVE Program
- CVE-2026-91920 · NVD
- FIRST EPSS
- GHSA-3f65-g3hr-c59r · GitHub Advisory Database · CC BY 4.0
- CVE-2026-91920 · Red Hat security data · CC BY 4.0
This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences