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CVE-2026-91920

Undertow: undertow: chunkreader message length permits chunk-size overflow

6.5 Medium

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.

Attack profile

How easy it is to exploit

Attack vector
Network
Complexity
Low
Privileges needed
None
User interaction
None

What an attacker can affect

Confidentiality
None
Integrity
Low
Availability
Low

Exploit likelihood

0.24%Unchanged since Oct 30, 2026
90%50%10%1%

What each source reports

CVE List Score used 6.5

Undertow: undertow: chunkreader message length permits chunk-size overflow

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.

Record
CVE-2026-91920
CVSS 3.1
6.5 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:L
Weakness
CWE-444
Updated
2026-11-06
EUVDEUVD-2026-113473 6.5

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.

Record
EUVD-2026-113473
CVSS 3.1
6.5 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:L
Updated
2026-11-06
GitHub AdvisoriesGHSA-3f65-g3hr-c59r 6.5

A flaw was found in the ChunkReader component of the Undertow web server, which is used to handle...

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.

Record
GHSA-3f65-g3hr-c59r
CVSS 3.1
6.5 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:L
Weakness
CWE-444
Updated
2026-11-02
NVD 6.5

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.

Record
CVE-2026-91920
CVSS 3.1
6.5 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:L
Weakness
CWE-444
Updated
2026-11-06
OSVDEBIAN-CVE-2026-91920 6.5

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.

Record
DEBIAN-CVE-2026-91920
CVSS 3.1
6.5 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:L
Updated
2026-11-04
OSVUBUNTU-CVE-2026-91920 6.5

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.

Record
UBUNTU-CVE-2026-91920
CVSS 3.1
6.5 MediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:L
Updated
2026-11-05

Affected products

Affected packages

Affected packages
PackageAffectedFixed
undertow
Debian:14
All versions, plus listed versions
1.3.11-11.3.16-11.3.19-11.3.21-11.3.23-1
Show 45 moreShow less
1.3.4-11.3.5-11.3.7-11.4.0-11.4.1-11.4.18-11.4.20-11.4.21-11.4.21-21.4.22-11.4.23-11.4.23-21.4.23-31.4.25-11.4.25-21.4.3-11.4.4-11.4.6-11.4.7-11.4.8-12.0.23-12.0.25-12.0.26-12.0.27-12.0.28-12.0.29-12.0.30-12.1.0-12.1.1-12.1.3-12.2.0-12.2.10-12.2.12-12.2.13-12.2.14-12.2.16-12.2.17-12.2.18-12.2.19-12.2.2-12.2.20-12.2.21-12.2.3-12.2.4-12.2.5-1
None known
undertow
Ubuntu:Pro:16.04:LTS
All versions, plus listed versions
1.3.4-11.3.5-11.3.7-11.3.11-11.3.16-11.3.16-1ubuntu0.1~esm1
None known
undertow
Ubuntu:Pro:18.04:LTS
All versions, plus listed versions
1.4.20-11.4.21-11.4.22-11.4.23-11.4.23-2build11.4.23-31.4.23-3ubuntu0.1~esm1
None known
undertow
Ubuntu:Pro:20.04:LTS
All versions, plus listed versions
2.0.23-12.0.27-12.0.28-12.0.29-12.0.29-1ubuntu0.1~esm1
None known
undertow
Ubuntu:Pro:22.04:LTS
All versions, plus listed versions
2.2.8-12.2.12-12.2.13-12.2.14-12.2.16-12.2.16-1ubuntu0.1~esm1
None known
undertow
Ubuntu:Pro:24.04:LTS
All versions, plus listed versions
2.3.8-22.3.8-2ubuntu0.1~esm1
None known
undertow
Ubuntu:26.10
All versions, plus listed versions
2.3.20-1ubuntu1
None known
undertow
Ubuntu:26.04:LTS
All versions, plus listed versions
2.3.18-22.3.20-12.3.20-1ubuntu1
None known

History

History
RecordedChangedSources
publishedEUVD, NVD, OSV
factsCVE List, EUVD, NVD, OSV
first indexedCVE List, EUVD, GitHub Advisories, NVD, OSV

Dates are when Every CVE recorded each change. Upstream dates may differ.

In short

CVE-2026-91920 is a medium vulnerability (CVSS 6.5) in Red Hat Build Of Apache Camel For Spring Boot 4, published October 30, 2026. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.24%, the 14th percentile. No source names a fixed version.

References

This page doesn't list everything

Left out here: 6 versions. The JSON record has them.

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