Server hang via nonprogressing OpenSSL TLS reads
Published Sep 16, 2021 · Updated Aug 4, 2024
Improper TLS packet validation in Apache Tomcat allows remote attackers to hang the application server with a crafted packet. OpenSSLEngine.unwrap accepted a zero-byte native read as normal loop termination even when OpenSSL reported pending plaintext, so processing could repeat without consuming input. The condition requires NIO or NIO2 with OpenSSL-backed TLS and affects 8.5.0 through 8.5.63, 9.0.0-M1 through 9.0.43, and 10.0.0-M1 through 10.0.2; the bounded consequence is a service hang.
Summary
What happened
Improper TLS packet validation in Apache Tomcat allows remote attackers to hang the application server with a crafted packet. OpenSSLEngine.unwrap accepted a zero-byte native read as normal loop termination even when OpenSSL reported pending plaintext, so processing could repeat without consuming input. The condition requires NIO or NIO2 with OpenSSL-backed TLS and affects 8.5.0 through 8.5.63, 9.0.0-M1 through 9.0.43, and 10.0.0-M1 through 10.0.2; the bounded consequence is a service hang.
The record
- CVE
- CVE-2021-41079
- Published
- Sep 16, 2021
- Updated
- Aug 4, 2024
- Vendor
- The Apache Software Foundation
- Product
- Apache Tomcat
- Classifications
- CWE-20, CWE-835, T1499.004
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Sep 16, 2021CVE publishedPublication date reported by the CVE source.
- Aug 4, 2024Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=Apache Tomcat 10 10.0.0-M1 to 10.0.2
- Affected versionversion=Apache Tomcat 8.5 8.5.0 to 8.5.63
- Affected versionversion=Apache Tomcat 9 9.0.0-M1 to 9.0.43
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
No public exploit references are available in this record.
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Technologies
Your stack
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Your stack
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