Medium 5.3HealthcarePublished Jul 12, 2021

CVE-2021-33037Incorrect Transfer-Encoding handling with HTTP/1.0

Updated under an hour ago (Oct 27, 2026, 9:00 AM ET)

Does this affect you?

It affects Apache Software Foundation Apache Tomcat and 22 other products. Add what you run to find out whether that includes you.

EPSS puts the chance of exploitation in the next 30 days at 74.67%, higher than 99% of scored CVEs. That is high: schedule it on your emergency patch path.

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Every CVE for Apache Software Foundation Apache Tomcat

Exploited in the last 30 days

Apache Tomcat 10.0.0-M1 to 10.0.6, 9.0.0.M1 to 9.0.46 and 8.5.0 to 8.5.66 did not correctly parse the HTTP transfer-encoding request header in some circumstances leading to the possibility to request smuggling when used with a reverse proxy. Specifically: - Tomcat incorrectly ignored the transfer encoding header if the client declared it would only accept an HTTP/1.0 response; - Tomcat honoured the identify encoding; and - Tomcat did not ensure that, if present, the chunked encoding was the final encoding.

CVSS: 5.3 MEDIUM (v3.1, NVD)CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
Weakness (CWE): CWE-444
Known exploited: Not in CISA's KEV catalog
EPSS (exploitation in the next 30 days): 74.67% (percentile 99)
Assigned by: apache
NVD analysis: Modified
Record last updated: Oct 8, 2026
First seen by InfoSec Signals: Oct 9, 2026

Affected products

Affected products

Apache Software Foundation Apache Tomcat apache_software_foundation:apache_tomcat (from the name)	Apache Tomcat 10 10.0.0-M1 to 10.0.6; Apache Tomcat 9 9.0.0.M1 to 9.0.46; Apache Tomcat 8 8.5.0 to 8.5.66	CNA record
apache tomcat apache:tomcat	from 8.5.0 through 8.5.66; after 9.0.0 through 9.0.46; after 10.0.0 through 10.0.6	NVD
apache tomee apache:tomee	8.0.6	NVD
debian debian_linux debian:debian_linux	9.0; 10.0	NVD
oracle agile_product_lifecycle_management oracle:agile_product_lifecycle_management	9.3.6	NVD
oracle communications_cloud_native_core_policy oracle:communications_cloud_native_core_policy	1.14.0	NVD
oracle communications_cloud_native_core_service_communication_proxy oracle:communications_cloud_native_core_service_communication_proxy	1.14.0	NVD
oracle communications_diameter_signaling_router oracle:communications_diameter_signaling_router	from 8.0.0.0 through 8.5.0.2	NVD
oracle communications_instant_messaging_server oracle:communications_instant_messaging_server	10.0.1.5.0	NVD
oracle communications_policy_management oracle:communications_policy_management	12.5.0	NVD
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References

References

https://lists.apache.org/thread.html/r612a79269b0d5e5780c62dfd34286a8037232fec0bc6f1a7e60c9381%40%3Cannounce.tomcat.apache.org%3E	x-refsource-misc, mailing-list, vendor-advisory
https://www.oracle.com//security-alerts/cpujul2021.html	x-refsource-misc, patch, third-party-advisory
https://lists.apache.org/thread.html/r40f921575aee8d7d34e53182f862c45cbb8f3d898c9d4e865c2ec262%40%3Ccommits.tomee.apache.org%3E	mailing-list, x-refsource-mlist
https://lists.apache.org/thread.html/re01e7e93154e8bdf78a11a23f9686427bd3d51fc6e12c508645567b7%40%3Ccommits.tomee.apache.org%3E	mailing-list, x-refsource-mlist
https://lists.debian.org/debian-lts-announce/2021/08/msg00009.html	mailing-list, x-refsource-mlist, third-party-advisory
https://www.debian.org/security/2021/dsa-4952	vendor-advisory, x-refsource-debian, third-party-advisory
https://lists.apache.org/thread.html/rd0dfea39829bc0606c936a16f6fca338127c86c0a1083970b45ac8d2%40%3Ccommits.tomee.apache.org%3E	mailing-list, x-refsource-mlist
https://lists.apache.org/thread.html/r290aee55b72811fd19e75ac80f6143716c079170c5671b96932ed44b%40%3Ccommits.tomee.apache.org%3E	mailing-list, x-refsource-mlist
https://lists.apache.org/thread.html/rf1b54fd3f52f998ca4829159a88cc4c23d6cef5c6447d00948e75c97%40%3Ccommits.tomee.apache.org%3E	mailing-list, x-refsource-mlist
https://lists.apache.org/thread.html/rc6ef52453bb996a98cb45442871a1db56b7c349939e45d829bf9ae37%40%3Ccommits.tomee.apache.org%3E	mailing-list, x-refsource-mlist
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The CVE record on cve.org NVD's entry

The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.