CVE-2021-42340 | DoS via memory leak with WebSocket connections

The fix for bug 63362 present in Apache Tomcat 10.1.0-M1 to 10.1.0-M5, 10.0.0-M1 to 10.0.11, 9.0.40 to 9.0.53 and 8.5.60 to 8.5.71 introduced a memory leak. The object introduced to collect metrics for HTTP upgrade connections was not released for WebSocket connections once the connection was closed. This created a memory leak that, over time, could lead to a denial of service via an OutOfMemoryError.

Published: 2021-10-14 Last update: 2024-11-21 Assigner: [email protected] Source: [email protected]

Conclusion & alert: CVE-2021-42340 is rated Moderate Risk (59.7/100): CVSS High severity, with medium exploitation likelihood (EPSS 4.28%). Mandatory action: Review affected assets and schedule remediation.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2021-42340

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-04-14 5.70% 4.28% -1.42%
2 2026-03-04 2.27% 5.70% +3.44%
3 2026-03-01 2.27%

Full EPSS history (58 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2021-42340

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
7.5 3.1 HIGH
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
3.9 3.6 [email protected]
5.0 2.0 MEDIUM
AV:N/AC:L/Au:N/C:N/I:N/A:P Click to expand
Access vector (AV:N)
Can be exploited remotely over network reachability.
Access complexity (AC:L)
Exploitation conditions are straightforward and predictable.
Authentication (AU:N)
No authentication is required.
Confidentiality impact (C:N)
No confidentiality impact.
Integrity impact (I:N)
No integrity impact.
Availability impact (A:P)
Partial availability impact.
10.0 2.9 [email protected]

Weakness enumeration for CVE-2021-42340

GitHub Security Advisory for CVE-2021-42340

GHSA-wph7-x527-w3h5 · Severity: high · Ecosystem: maven — Missing Release of Resource after Effective Lifetime in Apache Tomcat

OS Trackers for CVE-2021-42340

vendor priority summary link
debian not yet assigned CVE-2021-42340 not yet assigned priority: Debian including 1 source packages (tomcat9), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5. https://security-tracker.debian.org/tracker/CVE-2021-42340
gentoo low CVE-2021-42340: 1 GLSA(s) (202208-34), 1 atom(s) (www-servers/tomcat); latest impact low. https://bugs.gentoo.org/buglist.cgi?quicksearch=CVE-2021-42340
redhat high https://access.redhat.com/security/cve/CVE-2021-42340
ubuntu medium CVE-2021-42340 medium priority: Ubuntu including 2 source packages (tomcat8, tomcat9), 18 status rows across 14 suites (bionic, focal, hirsute, impish, jammy, kinetic, lunar, mantic, noble, oracular, plucky, trusty, upstream, xenial): ignored 9, not-affected 7, released 2. https://ubuntu.com/security/CVE-2021-42340

Affected software / configurations for CVE-2021-42340

Vendor Product Version Raw CPE
apache tomcat >= 8.5.60, < 8.5.72 cpe:2.3:a:apache:tomcat:*:*:*:*:*:*:*:*
apache tomcat >= 9.0.40, < 9.0.54 cpe:2.3:a:apache:tomcat:*:*:*:*:*:*:*:*
apache tomcat >= 10.0.1, < 10.0.12 cpe:2.3:a:apache:tomcat:*:*:*:*:*:*:*:*
apache tomcat 10.0.0 cpe:2.3:a:apache:tomcat:10.0.0:milestone10:*:*:*:*:*:*
apache tomcat 10.1.0 cpe:2.3:a:apache:tomcat:10.1.0:milestone1:*:*:*:*:*:*
apache tomcat 10.1.0 cpe:2.3:a:apache:tomcat:10.1.0:milestone2:*:*:*:*:*:*
apache tomcat 10.1.0 cpe:2.3:a:apache:tomcat:10.1.0:milestone3:*:*:*:*:*:*
apache tomcat 10.1.0 cpe:2.3:a:apache:tomcat:10.1.0:milestone4:*:*:*:*:*:*
apache tomcat 10.1.0 cpe:2.3:a:apache:tomcat:10.1.0:milestone5:*:*:*:*:*:*
netapp hci cpe:2.3:a:netapp:hci:-:*:*:*:*:*:*:*
netapp management_services_for_element_software cpe:2.3:a:netapp:management_services_for_element_software:-:*:*:*:*:*:*:*
debian debian_linux 11.0 cpe:2.3:o:debian:debian_linux:11.0:*:*:*:*:*:*:*
oracle agile_engineering_data_management 6.2.1.0 cpe:2.3:a:oracle:agile_engineering_data_management:6.2.1.0:*:*:*:*:*:*:*
oracle big_data_spatial_and_graph < 23.1 cpe:2.3:a:oracle:big_data_spatial_and_graph:*:*:*:*:*:*:*:*
oracle communications_diameter_signaling_router >= 8.0.0.0, <= 8.5.0.2 cpe:2.3:a:oracle:communications_diameter_signaling_router:*:*:*:*:*:*:*:*
oracle hospitality_cruise_shipboard_property_management_system 20.1.0 cpe:2.3:a:oracle:hospitality_cruise_shipboard_property_management_system:20.1.0:*:*:*:*:*:*:*
oracle managed_file_transfer 12.2.1.3.0 cpe:2.3:a:oracle:managed_file_transfer:12.2.1.3.0:*:*:*:*:*:*:*
oracle managed_file_transfer 12.2.1.4.0 cpe:2.3:a:oracle:managed_file_transfer:12.2.1.4.0:*:*:*:*:*:*:*
oracle middleware_common_libraries_and_tools 12.2.1.4.0 cpe:2.3:a:oracle:middleware_common_libraries_and_tools:12.2.1.4.0:*:*:*:*:*:*:*
oracle payment_interface 19.1 cpe:2.3:a:oracle:payment_interface:19.1:*:*:*:*:*:*:*
oracle payment_interface 20.3 cpe:2.3:a:oracle:payment_interface:20.3:*:*:*:*:*:*:*
oracle retail_customer_insights 15.0.2 cpe:2.3:a:oracle:retail_customer_insights:15.0.2:*:*:*:*:*:*:*
oracle retail_customer_insights 16.0.2 cpe:2.3:a:oracle:retail_customer_insights:16.0.2:*:*:*:*:*:*:*
oracle retail_data_extractor_for_merchandising 15.0.2 cpe:2.3:a:oracle:retail_data_extractor_for_merchandising:15.0.2:*:*:*:*:*:*:*
oracle retail_data_extractor_for_merchandising 16.0.2 cpe:2.3:a:oracle:retail_data_extractor_for_merchandising:16.0.2:*:*:*:*:*:*:*
oracle retail_eftlink 21.0.0 cpe:2.3:a:oracle:retail_eftlink:21.0.0:*:*:*:*:*:*:*
oracle retail_financial_integration 16.0.1 cpe:2.3:a:oracle:retail_financial_integration:16.0.1:*:*:*:*:*:*:*
oracle retail_financial_integration 19.0.0 cpe:2.3:a:oracle:retail_financial_integration:19.0.0:*:*:*:*:*:*:*
oracle retail_store_inventory_management 14.0.4.13 cpe:2.3:a:oracle:retail_store_inventory_management:14.0.4.13:*:*:*:*:*:*:*
oracle retail_store_inventory_management 14.1.3.5 cpe:2.3:a:oracle:retail_store_inventory_management:14.1.3.5:*:*:*:*:*:*:*
oracle retail_store_inventory_management 14.1.3.14 cpe:2.3:a:oracle:retail_store_inventory_management:14.1.3.14:*:*:*:*:*:*:*
oracle retail_store_inventory_management 15.0.3.3 cpe:2.3:a:oracle:retail_store_inventory_management:15.0.3.3:*:*:*:*:*:*:*
oracle retail_store_inventory_management 15.0.3.8 cpe:2.3:a:oracle:retail_store_inventory_management:15.0.3.8:*:*:*:*:*:*:*
oracle retail_store_inventory_management 16.0.3.7 cpe:2.3:a:oracle:retail_store_inventory_management:16.0.3.7:*:*:*:*:*:*:*
oracle sd-wan_edge 9.0 cpe:2.3:a:oracle:sd-wan_edge:9.0:*:*:*:*:*:*:*
oracle sd-wan_edge 9.1 cpe:2.3:a:oracle:sd-wan_edge:9.1:*:*:*:*:*:*:*
oracle taleo_platform cpe:2.3:a:oracle:taleo_platform:*:*:*:*:*:*:*:*

References for CVE-2021-42340

URL Tags
https://kc.mcafee.com/corporate/index?page=content&id=SB10379 Third Party Advisory
https://lists.apache.org/thread.html/r8097a2d1550aa78e585fc77e602b9046e6d4099d8d132497c5387784%40%3Ccommits.myfaces.apache.org%3E
https://lists.apache.org/thread.html/r83a35be60f06aca2065f188ee542b9099695d57ced2e70e0885f905c%40%3Cannounce.tomcat.apache.org%3E Mailing List Vendor Advisory
https://security.gentoo.org/glsa/202208-34 Third Party Advisory
https://security.netapp.com/advisory/ntap-20211104-0001/ Third Party Advisory
https://www.debian.org/security/2021/dsa-5009 Third Party Advisory
https://www.oracle.com/security-alerts/cpuapr2022.html Patch Third Party Advisory
https://www.oracle.com/security-alerts/cpujan2022.html Patch Third Party Advisory
https://www.oracle.com/security-alerts/cpujul2022.html Patch Third Party Advisory
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