7.5

CVE-2021-25122: Apache Tomcat h2c request mix-up

Modified
AliasesUBUNTU-CVE-2021-25122DEBIAN-CVE-2021-25122GHSA-j39c-c8hj-x4j3
Published 01-03-2021Last modified 08-10-2026

Vulnerability summary

CVE-2021-25122 is a high (CVSS 7.5) vulnerability in apache software foundation apache tomcat. EPSS estimates a 18.11% chance of exploitation in the next 30 days, higher than 97.2% of scored vulnerabilities.

Priority
Prioritisesevere

Severe, CVSS 7.5 (NVD); no exploitation reported by the 5 checked sources; EPSS 18% (FIRST, 03-11-2026)

Source freshness unavailable

How is this decided?
CVSS score
7.5/10
010
High · v3.1 (NVD)
EPSS score
18.11%
0%100%
Medium · 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 12
DLA-2594-1DSA-4891-1MGASA-2021-0357OPENSUSE-SU-2021:0496-1OPENSUSE-SU-2024:11468-1OPENSUSE-SU-2024:13441-1

Timeline

  1. 01-03-2021
    PublishedVulnerability first disclosed.
  2. 08-10-2026
    Last modifiedVulnerability information updated.

Description

When responding to new h2c connection requests, Apache Tomcat versions 10.0.0-M1 to 10.0.0, 9.0.0.M1 to 9.0.41 and 8.5.0 to 8.5.61 could duplicate request headers and a limited amount of request body from one request to another meaning user A and user B could both see the results of user A's request.

CVSS metrics

5 scores · 4 sources · 2 versions

EPSS trend

Probability

18.11%

Chance of exploitation in the next 30 days

Percentile

97%

Versus all other CVEs

30-day change

No change 0.00 pp

From 18.11% 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.

Oracle10 products
Debian2 products
Ubuntu2 products
  • tomcat8< 8.5.39-1ubuntu1~18.04.3+esm2
  • tomcat9< 9.0.16-3ubuntu0.18.04.2 | < 9.0.31-1ubuntu0.2
Apache1 product
  • tomcatEOL≥ 8.5.0, ≤ 8.5.61 | ≥ 9.0.0, ≤ 9.0.41 | 9.0.0:milestone1 | 9.0.0:milestone10 | 9.0.0:milestone11 | 9.0.0:milestone12 | 9.0.0:milestone13 | 9.0.0:milestone14 | 9.0.0:milestone15 | 9.0.0:milestone16 | 9.0.0:milestone17 | 9.0.0:milestone18 | 9.0.0:milestone19 | 9.0.0:milestone2 | 9.0.0:milestone20 | 9.0.0:milestone21 | 9.0.0:milestone22 | 9.0.0:milestone23 | 9.0.0:milestone24 | 9.0.0:milestone25 | 9.0.0:milestone26 | 9.0.0:milestone27 | 9.0.0:milestone3 | 9.0.0:milestone4 | 9.0.0:milestone5 | 10.0.0 | 10.0.0:milestone1 | 10.0.0:milestone10 | 10.0.0:milestone2 | 10.0.0:milestone3 | 10.0.0:milestone4 | 10.0.0:milestone5 | 10.0.0:milestone6 | 10.0.0:milestone7 | 10.0.0:milestone8 | 10.0.0:milestone9
Apache software foundation1 product
  • apache tomcat≥ Apache Tomcat 10, < 10.0.2 | ≥ Apache Tomcat 9, < 9.0.42 | ≥ Apache Tomcat 8.5, < 8.5.62
Org.apache.tomcat1 product
  • tomcat-coyote≥ 10.0.0-M1, < 10.0.2
Org.apache.tomcat.embed1 product
  • tomcat-embed-core≥ 10.0.0-M1, < 10.0.2 | ≥ 9.0.0-M1, < 9.0.43 | ≥ 8.5.0, < 8.5.63

7 vendors · 18 products

References

31 links
Show all 31 references