5.3

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

Modified
AliasesUBUNTU-CVE-2021-33037DEBIAN-CVE-2021-33037GHSA-4vww-mc66-62m6
Published 12-07-2021Last modified 08-10-2026

Vulnerability summary

CVE-2021-33037 is a medium (CVSS 5.3) vulnerability in apache software foundation apache tomcat. EPSS estimates a 74.67% chance of exploitation in the next 30 days, higher than 99.5% of scored vulnerabilities.

Priority
Routine

Not severe (CVSS 5.3, network access); no exploitation reported by the 5 checked sources

Source freshness unavailable

How is this decided?
CVSS score
5.3/10
010
Medium · v3.1 (NVD)
EPSS score
74.67%
0%100%
Critical · 0.00 pp in 30 days
KEVNot listedNot listed by any tracked catalog.
RansomwareNot flaggedNo ransomware use recorded.
Public exploits0No public exploits recorded

Advisory lineage

Upstream 0 · Downstream 14 · Related 10
DLA-2733-1DSA-4952-1MGASA-2021-0485OPENSUSE-SU-2021:1490-1OPENSUSE-SU-2021:3672-1OPENSUSE-SU-2024:11618-1

Timeline

  1. 12-07-2021
    PublishedVulnerability first disclosed.
  2. 08-10-2026
    Last modifiedVulnerability information updated.

Description

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 metrics

5 scores · 4 sources · 2 versions

EPSS trend

Probability

74.67%

Chance of exploitation in the next 30 days

Percentile

100%

Versus all other CVEs

30-day change

No change 0.00 pp

From 74.67% on 04-10-2026

04-10-202603-11-2026

Known exploited

Compare KEV catalogs
CISA KEV

Not in the CISA KEV catalog.

ENISA CNW

Not in the ENISA CNW catalog.

CIRCL

Not in the CIRCL catalog.

Public exploits

0 found

No public exploits indexed.

Weaknesses

CWE · root cause

Affected systems

Version check

Known conditions: network-reachable, no authentication, no user interaction (CVSS vector). Other conditions: not stated in public data.

Oracle18 products
Ubuntu4 products
  • tomcat6All versions (No fix recorded)
  • tomcat7All versions (No fix recorded)
  • tomcat8All versions (No fix recorded)
  • tomcat9< 9.0.16-3ubuntu0.18.04.2 | < 9.0.31-1ubuntu0.2
Apache2 products
  • tomcat≥ 8.5.0, ≤ 8.5.66 | > 9.0.0, ≤ 9.0.46 | > 10.0.0, ≤ 10.0.6
  • tomee8.0.6
Debian2 products
Apache software foundation1 product
  • apache tomcatApache 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
Mcafee1 product
  • epolicy_orchestrator< 5.10.0 | 5.10.0 | 5.10.0:update_1 | 5.10.0:update_10 | 5.10.0:update_2 | 5.10.0:update_3 | 5.10.0:update_4 | 5.10.0:update_5 | 5.10.0:update_6 | 5.10.0:update_7 | 5.10.0:update_8 | 5.10.0:update_9
Org.apache.tomcat1 product
  • tomcat≥ 10.0.0-M1, < 10.0.7 | ≥ 9.0.0-M1, < 9.0.48 | ≥ 8.5.0, < 8.5.68

7 vendors · 29 products

References

42 links
Show all 42 references