Summary
Concurrent Execution using Shared Resource with Improper Synchronization in Apache Tomcat
A bug in the error handling of the send file code for the NIO HTTP connector in Apache Tomcat 9.0.0.M1 to 9.0.0.M13, 8.5.0 to 8.5.8, 8.0.0.RC1 to 8.0.39, 7.0.0 to 7.0.73 and 6.0.16 to 6.0.48 resulted in the current Processor object being added to the Processor cache multiple times. This in turn meant that the same Processor could be used for concurrent requests. Sharing a Processor can result in information leakage between requests including, not not limited to, session ID and the response body. The bug was first noticed in 8.5.x onwards where it appears the refactoring of the Connector code for 8.5.x onwards made it more likely that the bug was observed. Initially it was thought that the 8.5.x refactoring introduced the bug but further investigation has shown that the bug is present in all currently supported Tomcat versions.
Impact
Multiple concurrent operations access a shared resource without proper synchronization, producing unpredictable results depending on timing. Typical impact: TOCTOU exploits, data corruption, or privilege escalation.
CVE-2016-8745 has a CVSS score of 7.5 (High). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (9.0.0.M14, 8.5.9, 8.0.41, 7.0.75, 6.0.50); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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org.apache.tomcat:tomcat-util to 9.0.0.M14 or later; org.apache.tomcat:tomcat-util to 8.5.9 or later; org.apache.tomcat:tomcat-util to 8.0.41 or later; org.apache.tomcat:tomcat-util to 7.0.75 or later; org.apache.tomcat:tomcat-util to 6.0.50 or later
Kodem Kai can prioritize this vulnerability in your dependency tree and generate a fix recommendation.
Frequently Asked Questions
- What is CVE-2016-8745? CVE-2016-8745 is a high-severity race condition vulnerability in org.apache.tomcat:tomcat-util (maven), affecting versions >= 9.0.0.M1, <= 9.0.0.M13. It is fixed in 9.0.0.M14, 8.5.9, 8.0.41, 7.0.75, 6.0.50. Multiple concurrent operations access a shared resource without proper synchronization, producing unpredictable results depending on timing.
- How severe is CVE-2016-8745? CVE-2016-8745 has a CVSS score of 7.5 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of org.apache.tomcat:tomcat-util are affected by CVE-2016-8745? org.apache.tomcat:tomcat-util (maven) versions >= 9.0.0.M1, <= 9.0.0.M13 is affected.
- Is there a fix for CVE-2016-8745? Yes. CVE-2016-8745 is fixed in 9.0.0.M14, 8.5.9, 8.0.41, 7.0.75, 6.0.50. Upgrade to this version or later.
- Is CVE-2016-8745 exploitable, and should I be worried? Whether CVE-2016-8745 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2016-8745 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2016-8745?
- Upgrade
org.apache.tomcat:tomcat-utilto 9.0.0.M14 or later - Upgrade
org.apache.tomcat:tomcat-utilto 8.5.9 or later - Upgrade
org.apache.tomcat:tomcat-utilto 8.0.41 or later - Upgrade
org.apache.tomcat:tomcat-utilto 7.0.75 or later - Upgrade
org.apache.tomcat:tomcat-utilto 6.0.50 or later
- Upgrade