CVE-2019-15225 in Envoy
Summary
by MITRE
In Envoy through 1.11.1, users may configure a route to match incoming path headers via the libstdc++ regular expression implementation. A remote attacker may send a request with a very long URI to result in a denial of service (memory consumption). This is a related issue to CVE-2019-14993.
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Analysis
by VulDB Data Team • 11/27/2023
The vulnerability CVE-2019-15225 affects the Envoy proxy software version 1.11.1 and earlier, representing a significant denial of service weakness that stems from improper handling of regular expression patterns in path header matching. This issue specifically involves the integration of libstdc++ regular expression implementation within Envoy's routing configuration system, where users can define routes that match incoming HTTP path headers using regular expressions. The flaw becomes exploitable when a remote attacker crafts malicious requests with excessively long URIs that trigger memory exhaustion during regex processing. The vulnerability is categorized under CWE-400 as an unspecified vulnerability related to resource exhaustion, specifically manifesting as memory consumption issues. This weakness allows attackers to consume excessive system resources through carefully crafted URI patterns, effectively rendering the target system unavailable to legitimate users.
The technical implementation of this vulnerability occurs when Envoy processes incoming HTTP requests that contain path headers matching configured routes using libstdc++ regular expressions. When a maliciously long URI is presented to the system, the regex engine attempts to process the pattern matching operation, leading to exponential memory consumption growth. This behavior is characteristic of regex denial of service attacks where the complexity of pattern matching increases dramatically with input size, particularly when the regular expression engine encounters patterns that cause backtracking or resource-intensive operations. The exploitation mechanism relies on the specific characteristics of libstdc++'s regex implementation, which may not properly handle pathological input cases that would otherwise be rejected by more robust regex engines. This vulnerability operates at the application layer, specifically within the HTTP routing and header processing components of Envoy's proxy functionality.
The operational impact of CVE-2019-15225 extends beyond simple service disruption, as it can lead to complete system unavailability and resource exhaustion across multiple Envoy instances. When exploited successfully, the vulnerability allows attackers to consume all available memory on the target system, causing the proxy to crash or become unresponsive, thereby blocking legitimate traffic and potentially affecting downstream services that depend on the proxy for traffic management. The attack requires minimal privileges and can be executed through simple HTTP requests, making it particularly dangerous in production environments where Envoy serves as a critical traffic management component. The vulnerability affects systems where regular expression matching is enabled for path headers, which is a common configuration in complex routing scenarios involving microservices architectures or API gateways that utilize Envoy as their primary proxy solution. This weakness is particularly concerning in cloud-native environments where Envoy is deployed extensively and may be exposed to untrusted traffic sources.
Mitigation strategies for CVE-2019-15225 should focus on both immediate defensive measures and long-term architectural improvements. The primary recommendation involves upgrading to Envoy version 1.11.2 or later, where the vulnerability has been addressed through improved input validation and regex processing. Organizations should also implement request size limits and URI length restrictions at the proxy level to prevent maliciously long URIs from reaching the regex processing components. Network-level controls such as rate limiting and connection throttling can help reduce the impact of exploitation attempts. Additionally, implementing proper regex engine configuration that limits backtracking and sets maximum execution time for pattern matching operations provides additional protection layers. From a defensive perspective, this vulnerability aligns with ATT&CK technique T1499.004 for resource exhaustion attacks and demonstrates the importance of proper input validation and regular expression security practices. Organizations should conduct thorough testing of their Envoy configurations to ensure that regex patterns are appropriately bounded and that no overly complex patterns are being used in production environments. The vulnerability also highlights the necessity of following security best practices for regular expression usage as outlined in industry standards and security frameworks.