CVE-2016-8745 in Tomcat
Summary
by MITRE
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.
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Analysis
by VulDB Data Team • 10/05/2022
The vulnerability identified as CVE-2016-8745 represents a critical flaw in Apache Tomcat's NIO HTTP connector implementation that affects multiple versions across the 6.x, 7.x, 8.x, and 9.x release lines. This issue stems from improper error handling within the file sending code that leads to a fundamental architectural failure in request processing. The bug manifests when the Processor object, which handles individual HTTP requests, gets added to the Processor cache multiple times during error conditions. This duplication creates a scenario where the same Processor instance can be concurrently assigned to handle multiple requests simultaneously, fundamentally compromising the isolation that should exist between individual HTTP transactions.
The technical nature of this vulnerability aligns with CWE-362, which describes concurrent execution using shared resource vulnerabilities, and specifically relates to improper handling of shared resources in multi-threaded environments. The flaw operates at the core of Tomcat's request processing pipeline where the Processor cache mechanism fails to properly manage object lifecycle during error conditions. When an error occurs during file transmission, the error handling code path incorrectly adds the same Processor object to the cache multiple times, creating a race condition where identical Processor instances are reused across different request contexts. This architectural weakness was exacerbated by the refactoring efforts in the 8.5.x branch, though investigation revealed the vulnerability existed across all supported versions, indicating a deeper systemic issue in how Processor objects are managed during error scenarios.
The operational impact of this vulnerability is severe and directly threatens the confidentiality and integrity of web applications running on affected Tomcat versions. When multiple requests share the same Processor object, sensitive information can become intertwined between concurrent transactions, leading to session ID leakage, response body contamination, and potential data cross-contamination. Attackers could exploit this vulnerability to access session information from other users, potentially leading to session hijacking attacks where authentication tokens and user-specific data become accessible to unauthorized parties. The vulnerability affects the fundamental security model of web applications by breaking the expected isolation between HTTP requests, allowing for information leakage that could compromise user privacy and application security. The issue is particularly concerning in environments where multiple concurrent requests are common, as the probability of encountering the race condition increases significantly.
Mitigation strategies for CVE-2016-8745 require immediate attention and should include upgrading to patched versions of Apache Tomcat where the Processor cache management has been corrected to prevent duplicate additions. Organizations should prioritize updating their Tomcat installations to versions that address this specific error handling issue, as the vulnerability exists across multiple major versions and affects the core functionality of the application server. Additionally, implementing proper monitoring and logging of Processor cache behavior can help detect anomalous patterns that might indicate the vulnerability is being exploited. Security teams should also consider deploying network-based intrusion detection systems that can monitor for suspicious session behavior or unusual response patterns that might indicate information leakage. The fix implemented in patched versions addresses the root cause by ensuring that Processor objects are properly removed from the cache before being added again during error handling, preventing the reuse of the same object across concurrent requests. This remediation aligns with ATT&CK technique T1566 which involves credential access through exploitation of software vulnerabilities, specifically targeting the information disclosure aspect of this vulnerability.