CVE Vulnerabilities

CVE-2021-43980

Concurrent Execution using Shared Resource with Improper Synchronization ('Race Condition')

Published: Sep 28, 2022 | Modified: May 21, 2025
CVSS 3.x
3.7
LOW
Source:
NVD
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N
CVSS 2.x
RedHat/V2
RedHat/V3
3.7 LOW
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N
Ubuntu
MEDIUM
root.io logo minimus.io logo echo.ai logo

The simplified implementation of blocking reads and writes introduced in Tomcat 10 and back-ported to Tomcat 9.0.47 onwards exposed a long standing (but extremely hard to trigger) concurrency bug in Apache Tomcat 10.1.0 to 10.1.0-M12, 10.0.0-M1 to 10.0.18, 9.0.0-M1 to 9.0.60 and 8.5.0 to 8.5.77 that could cause client connections to share an Http11Processor instance resulting in responses, or part responses, to be received by the wrong client.

Weakness

The product contains a concurrent code sequence that requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence operating concurrently.

Affected Software

NameVendorStart VersionEnd Version
TomcatApache8.5.0 (including)8.5.77 (including)
TomcatApache9.0.0 (including)9.0.60 (including)
TomcatApache10.0.0 (including)10.0.18 (including)
TomcatApache10.1.0-milestone1 (including)10.1.0-milestone1 (including)
TomcatApache10.1.0-milestone10 (including)10.1.0-milestone10 (including)
TomcatApache10.1.0-milestone11 (including)10.1.0-milestone11 (including)
TomcatApache10.1.0-milestone12 (including)10.1.0-milestone12 (including)
TomcatApache10.1.0-milestone2 (including)10.1.0-milestone2 (including)
TomcatApache10.1.0-milestone3 (including)10.1.0-milestone3 (including)
TomcatApache10.1.0-milestone4 (including)10.1.0-milestone4 (including)
TomcatApache10.1.0-milestone5 (including)10.1.0-milestone5 (including)
TomcatApache10.1.0-milestone6 (including)10.1.0-milestone6 (including)
TomcatApache10.1.0-milestone7 (including)10.1.0-milestone7 (including)
TomcatApache10.1.0-milestone8 (including)10.1.0-milestone8 (including)
TomcatApache10.1.0-milestone9 (including)10.1.0-milestone9 (including)
JWS 5.7.0RedHat*
Red Hat JBoss Web Server 5.7 on RHEL 7RedHatjws5-ecj-0:4.20.0-1.redhat_00002.1.el7jws*
Red Hat JBoss Web Server 5.7 on RHEL 7RedHatjws5-tomcat-0:9.0.62-9.redhat_00005.1.el7jws*
Red Hat JBoss Web Server 5.7 on RHEL 7RedHatjws5-tomcat-native-0:1.2.31-10.redhat_10.el7jws*
Red Hat JBoss Web Server 5.7 on RHEL 8RedHatjws5-ecj-0:4.20.0-1.redhat_00002.1.el8jws*
Red Hat JBoss Web Server 5.7 on RHEL 8RedHatjws5-tomcat-0:9.0.62-9.redhat_00005.1.el8jws*
Red Hat JBoss Web Server 5.7 on RHEL 8RedHatjws5-tomcat-native-0:1.2.31-10.redhat_10.el8jws*
Red Hat JBoss Web Server 5.7 on RHEL 9RedHatjws5-0:1-8.el9jws*
Red Hat JBoss Web Server 5.7 on RHEL 9RedHatjws5-ecj-0:4.20.0-1.redhat_00002.1.el9jws*
Red Hat JBoss Web Server 5.7 on RHEL 9RedHatjws5-javapackages-tools-0:3.4.1-5.15.11.el9jws*
Red Hat JBoss Web Server 5.7 on RHEL 9RedHatjws5-jboss-logging-0:3.4.1-1.Final_redhat_00001.1.el9jws*
Red Hat JBoss Web Server 5.7 on RHEL 9RedHatjws5-mod_cluster-0:1.4.3-2.Final_redhat_00002.1.el9jws*
Red Hat JBoss Web Server 5.7 on RHEL 9RedHatjws5-tomcat-0:9.0.62-9.redhat_00005.1.el9jws*
Red Hat JBoss Web Server 5.7 on RHEL 9RedHatjws5-tomcat-native-0:1.2.31-10.redhat_10.el9jws*
Red Hat JBoss Web Server 5.7 on RHEL 9RedHatjws5-tomcat-vault-0:1.1.8-4.Final_redhat_00004.1.el9jws*
Tomcat6Ubuntutrusty*
Tomcat6Ubuntutrusty/esm*
Tomcat6Ubuntuupstream*
Tomcat6Ubuntuxenial*
Tomcat7Ubuntubionic*
Tomcat7Ubuntutrusty*
Tomcat7Ubuntutrusty/esm*
Tomcat7Ubuntuupstream*
Tomcat7Ubuntuxenial*
Tomcat8Ubuntubionic*
Tomcat8Ubuntuesm-apps/bionic*
Tomcat8Ubuntuupstream*
Tomcat8Ubuntuxenial*
Tomcat9Ubuntubionic*
Tomcat9Ubuntuesm-apps/bionic*
Tomcat9Ubuntuesm-apps/focal*
Tomcat9Ubuntuesm-apps/jammy*
Tomcat9Ubuntufocal*
Tomcat9Ubuntujammy*
Tomcat9Ubuntukinetic*
Tomcat9Ubuntulunar*
Tomcat9Ubuntumantic*
Tomcat9Ubuntuoracular*
Tomcat9Ubuntuupstream*

Extended Description

A race condition occurs within concurrent environments, and it is effectively a property of a code sequence. Depending on the context, a code sequence may be in the form of a function call, a small number of instructions, a series of program invocations, etc. A race condition violates these properties, which are closely related:

A race condition exists when an “interfering code sequence” can still access the shared resource, violating exclusivity. The interfering code sequence could be “trusted” or “untrusted.” A trusted interfering code sequence occurs within the product; it cannot be modified by the attacker, and it can only be invoked indirectly. An untrusted interfering code sequence can be authored directly by the attacker, and typically it is external to the vulnerable product.

Potential Mitigations

  • Minimize the usage of shared resources in order to remove as much complexity as possible from the control flow and to reduce the likelihood of unexpected conditions occurring.
  • Additionally, this will minimize the amount of synchronization necessary and may even help to reduce the likelihood of a denial of service where an attacker may be able to repeatedly trigger a critical section (CWE-400).

References