CVE-2023-32731 in grpc
Summary
by MITRE • 06/09/2023
When gRPC HTTP2 stack raised a header size exceeded error, it skipped parsing the rest of the HPACK frame. This caused any HPACK table mutations to also be skipped, resulting in a desynchronization of HPACK tables between sender and receiver. If leveraged, say, between a proxy and a backend, this could lead to requests from the proxy being interpreted as containing headers from different proxy clients - leading to an information leak that can be used for privilege escalation or data exfiltration. We recommend upgrading beyond the commit contained in https://github.com/grpc/grpc/pull/32309 https://github.com/grpc/grpc/pull/32309
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Analysis
by VulDB Data Team • 12/04/2024
The vulnerability identified as CVE-2023-32731 resides within the gRPC HTTP/2 stack implementation, specifically addressing how the system handles header size exceeded errors during HPACK frame processing. This flaw represents a critical desynchronization issue in the HTTP/2 protocol implementation that can lead to severe security implications. The vulnerability manifests when the gRPC stack encounters a header size limit violation, causing it to prematurely terminate HPACK frame parsing without completing the necessary table mutation operations.
The technical root cause of this vulnerability can be categorized under CWE-129, which deals with insufficient validation of length of input data, and more specifically relates to CWE-200, which addresses information exposure. When a header size exceeds the configured limits, the gRPC implementation skips the parsing of subsequent HPACK table modifications, creating a fundamental mismatch between the sender and receiver's HPACK tables. This desynchronization occurs because HPACK table updates are essential for maintaining proper state synchronization between client and server during HTTP/2 communication.
The operational impact of this vulnerability extends beyond simple parsing errors to create significant security risks within proxy environments. When deployed in proxy architectures, this flaw allows malicious actors to exploit the desynchronized HPACK tables to inject or manipulate header information from different client sessions. The consequence is that requests passing through a proxy may be interpreted as containing headers belonging to other proxy clients, effectively enabling cross-client information leakage. This information leak can be leveraged for privilege escalation attacks where an attacker might gain access to data or capabilities belonging to other authenticated users.
The attack vector for this vulnerability typically involves a man-in-the-middle position within a proxy chain, where an attacker can manipulate the communication flow to exploit the HPACK desynchronization. The ATT&CK framework categorizes this as a technique involving information gathering and credential access through protocol manipulation. The vulnerability affects systems where gRPC proxies are used to forward requests between clients and backend services, making it particularly dangerous in enterprise environments where such proxy configurations are common.
Mitigation strategies should focus on immediate patching of the gRPC implementation to the version containing the fix referenced in the pull requests mentioned in the advisory. Organizations should prioritize upgrading their gRPC components beyond the commit referenced in https://github.com/grpc/grpc/pull/32309. Additionally, implementing proper header size validation at multiple layers of the network stack, including proxy configurations and load balancer settings, can provide additional defense-in-depth measures. Network monitoring should be enhanced to detect anomalous HPACK table behavior and header size violations that might indicate exploitation attempts. The fix addresses the core issue by ensuring that HPACK table mutations are properly processed even when header size limits are exceeded, preventing the desynchronization that leads to information leakage and potential privilege escalation.