CVE Intelligence
Medium Injection

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

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.

Published Jul 12, 2021 · Updated Oct 13, 2026 · Sources: NIST National Vulnerability Database, CVE Program (cve.org) e CISA ADP · CNA: apache

Who exploits it and how urgent it is

A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.

No exploitation signal in the sources consulted so far.
How the score was calculated
  • EPSS 74.7% (30-day exploitation probability)+15
  • Technical severity (medium)+3
  • Automatable exploitation (SSVC)+3

The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.

Exploitation
Not confirmed
Not in CISA KEV — an absence of record, not proof it is unexploited.
EPSS FIRST
74.67%
ahead of 99% of scored CVEs · Oct 14, 2026
Affects
Apache Software Foundation
Tomcat and 21 more
CVSS base
5.3
Medium · 1 source(s)

CISA SSVC assessment CISA

Three decision points CISA publishes for the CVEs it assesses (SSVC 2.0.3). A stakeholder decision, not a severity score.

Exploitation
None
none · proof-of-concept · active
Automatable
Yes
can an attacker script the kill-chain steps
Technical impact
Partial
partial · total control of the vulnerable component

Remediation

Fixes and mitigations documented by the sources — linked to the original advisory.

  • Documented patch — www.oracle.com (NIST National Vulnerability Database)
  • Documented patch — www.oracle.com (NIST National Vulnerability Database)
  • Documented patch — www.oracle.com (NIST National Vulnerability Database)
  • Documented patch — www.oracle.com (NIST National Vulnerability Database)

First 24 hours

Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.

  1. Identify exposed assets running the affected vendor/product/version combinations (Apache Software Foundation Tomcat, Apache Software Foundation Tomee, Debian Debian Linux…).
  2. The attack is network-based and needs no privileges: restrict exposure (ACLs, VPN, WAF) until patched.
  3. Apply the fixed version or the patch documented under Remediation.
  4. EPSS ahead of 99% of scored CVEs: prioritize it in the patch queue.
  5. Search available logs for exploit probes matching the vulnerability class (injection), errors and authentication anomalies.

Affected scope

Vendor, product and versions as the sources word them.

VendorProductVersionsStatusSource
Apache Software Foundation Tomcat version Apache Tomcat 8 8.5.0 to 8.5.66version Apache Tomcat 10 10.0.0-M1 to 10.0.6version Apache Tomcat 9 9.0.0.M1 to 9.0.46 Vulnerable CVE Program (cve.org) e CISA ADP
Apache Software Foundation Tomcat ≥ 8.5.0 and ≤ 8.5.66> 9.0.0 and ≤ 9.0.46> 10.0.0 and ≤ 10.0.6 Vulnerable NIST National Vulnerability Database
Apache Software Foundation Tomee version 8.0.6 Vulnerable NIST National Vulnerability Database
Debian Debian Linux version 10.0version 9.0 Vulnerable NIST National Vulnerability Database
Mcafee Epolicy Orchestrator < 5.10.0version 5.10.0-update_9version 5.10.0version 5.10.0-update_1version 5.10.0-update_10version 5.10.0-update_8version 5.10.0-update_7version 5.10.0-update_6
and 4 more version 5.10.0-update_2version 5.10.0-update_5version 5.10.0-update_4version 5.10.0-update_3
Vulnerable NIST National Vulnerability Database
Oracle Agile Product Lifecycle Management version 9.3.6 Vulnerable NIST National Vulnerability Database
Oracle Communications Cloud Native Core Policy version 1.14.0 Vulnerable NIST National Vulnerability Database
Oracle Communications Cloud Native Core Service Communication Proxy version 1.14.0 Vulnerable NIST National Vulnerability Database
Oracle Communications Diameter Signaling Router ≥ 8.0.0.0 and ≤ 8.5.0.2 Vulnerable NIST National Vulnerability Database
Oracle Communications Instant Messaging Server version 10.0.1.5.0 Vulnerable NIST National Vulnerability Database
Oracle Communications Policy Management version 12.5.0 Vulnerable NIST National Vulnerability Database
Oracle Communications Pricing Design Center version 12.0.0.3.0 Vulnerable NIST National Vulnerability Database
Oracle Communications Session Report Manager ≥ 8.0.0 and ≤ 8.2.4.0 Vulnerable NIST National Vulnerability Database
Oracle Communications Session Route Manager ≥ 8.0.0 and ≤ 8.2.4 Vulnerable NIST National Vulnerability Database
Oracle Graph Server And Client < 21.4 Vulnerable NIST National Vulnerability Database
Oracle Healthcare Translational Research version 4.1.0 Vulnerable NIST National Vulnerability Database
Oracle Hospitality Cruise Shipboard Property Management System version 20.1.0 Vulnerable NIST National Vulnerability Database
Oracle Instantis Enterprisetrack version 17.3version 17.2version 17.1 Vulnerable NIST National Vulnerability Database
Oracle Managed File Transfer version 12.2.1.3.0version 12.2.1.4.0 Vulnerable NIST National Vulnerability Database
Oracle Mysql Enterprise Monitor ≤ 8.0.25 Vulnerable NIST National Vulnerability Database
Oracle Sd-wan Edge version 9.1version 9.0 Vulnerable NIST National Vulnerability Database
Oracle Secure Global Desktop version 5.6 Vulnerable NIST National Vulnerability Database
Oracle Utilities Testing Accelerator version 6.0.0.3.1version 6.0.0.2.2version 6.0.0.1.1 Vulnerable NIST National Vulnerability Database

Attack characteristics

The CVSS vector, decoded. It describes the attack, not your exposure to it.

Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
Low
Availability
None

Every base score collected

Sources score independently and may disagree; each row says who scored it and under which version.

ScoreVersionSeverityExpl.ImpactScored by
5.3 CVSS 3.1 Medium 3.9 1.4 nvd@nist.gov via NIST National Vulnerability Database
5.0 CVSS 2.0 Medium 10.0 2.9 nvd@nist.gov via NIST National Vulnerability Database
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N (score shown at the top: nvd@nist.gov)

Weakness MITRE

Weakness class according to MITRE’s CWE catalog.

CWE-444 · HTTP Request Smuggling

Other CVEs with this weakness →

EPSS over time FIRST

Oct 13, 2026 → Oct 14, 2026 · 2 reading(s) · max 74.67%

Detection

Read off the CVSS vector and the weakness class. Starting points, not tested rules.

  • Prioritize edge telemetry for the network-reachable component (proxy, WAF, IDS/IPS).
  • Look for parameters with command/query metacharacters and unexpected child processes of the service.
web/proxy/WAF logsnetwork IDS/IPSapplication logsendpoint telemetry (EDR)

Timeline

What happened to this CVE, newest first.

  • 2026
  • Affected products added · apache software foundation/apache tomcat
    Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
  • SSVC assessment updated
    Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
  • Record published
    Oct 13, 2026
  • Fix documented
    Oct 13, 2026 · NIST National Vulnerability Database
  • CVSS changed · 5.3
    Oct 13, 2026 · NIST National Vulnerability Database
  • Source status changed · → Modified
    Oct 13, 2026 · NIST National Vulnerability Database
  • Record created in this database
    Oct 13, 2026 · NIST National Vulnerability Database
  • 2021
  • CVE published
    Jul 12, 2021 · apache

Source activity

Repeated readings are counted rather than listed.

  • 1× Official description updated · Oct 13, 2026 – Oct 13, 2026

References

16 on the record

Elsewhere on this site

Apache Software Foundation
every CVE for this vendor
Injection
same class
CWE-444
other pages naming this weakness

Related CVEs (same products)

  • CVE-2026-87266 Improper Access Control in Oracle Agile Product Lifecycle Management Sep 15, 2026
  • CVE-2026-87258 Improper Access Control in Oracle Agile Product Lifecycle Management Sep 15, 2026
  • CVE-2026-87257 Improper Access Control in Oracle Agile Product Lifecycle Management Sep 15, 2026
  • CVE-2026-87256 Improper Access Control in Oracle Agile Product Lifecycle Management Sep 15, 2026
  • CVE-2026-87254 Improper Access Control in Oracle Agile Product Lifecycle Management Sep 15, 2026
  • CVE-2026-87253 Improper Access Control in Oracle Agile Product Lifecycle Management Sep 15, 2026

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

  • No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
  • No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
  • No exploit packet captures, log samples, or incident case IDs supplied.

Answered from this record

Text assembled only from the fields above — no additional claims.

What should defenders know first?

CVE-2021-33037 is "Incorrect Transfer-Encoding handling with HTTP/1.0", rated Medium. It affects Tomcat (Apache Software Foundation); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 5.3 describes technical severity. EPSS 74.67% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.

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