CVE-2023-52775 in Linux
Summary
by MITRE • 05/21/2024
In the Linux kernel, the following vulnerability has been resolved:
net/smc: avoid data corruption caused by decline
We found a data corruption issue during testing of SMC-R on Redis applications.
The benchmark has a low probability of reporting a strange error as shown below.
"Error: Protocol error, got "\xe2" as reply type byte"
Finally, we found that the retrieved error data was as follows:
0xE2 0xD4 0xC3 0xD9 0x04 0x00 0x2C 0x20 0xA6 0x56 0x00 0x16 0x3E 0x0C 0xCB 0x04 0x02 0x01 0x00 0x00 0x20 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0xE2
It is quite obvious that this is a SMC DECLINE message, which means that the applications received SMC protocol message. We found that this was caused by the following situations:
client server ¦ clc proposal -------------> ¦ clc accept <------------- ¦ clc confirm -------------> wait llc confirm send llc confirm ¦failed llc confirm ¦ x------ (after 2s)timeout wait llc confirm rsp
wait decline
(after 1s) timeout (after 2s) timeout ¦ decline --------------> ¦ decline <--------------
As a result, a decline message was sent in the implementation, and this message was read from TCP by the already-fallback connection.
This patch double the client timeout as 2x of the server value, With this simple change, the Decline messages should never cross or collide (during Confirm link timeout).
This issue requires an immediate solution, since the protocol updates involve a more long-term solution.
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Analysis
by VulDB Data Team • 08/08/2026
The vulnerability CVE-2023-52775 affects the Linux kernel's SMC-R (Scalable Memory Communication - Reliable) implementation, specifically addressing a data corruption issue that occurs during the SMC protocol handshake process. This flaw manifests in Redis applications where corrupted data is transmitted, resulting in protocol errors with the specific error message "Error: Protocol error, got "�" as reply type byte." The issue stems from improper handling of SMC decline messages during connection establishment, where timing conflicts between client and server timeout mechanisms cause protocol messages to be incorrectly processed. The corrupted data pattern reveals a clear SMC DECLINE message structure with byte sequences indicating protocol-level interference, demonstrating that applications received SMC protocol messages instead of expected application data. This vulnerability operates at the network protocol level and represents a significant concern for systems relying on SMC-R for high-performance communication, as it can lead to complete application failures and data integrity issues.
The technical root cause of this vulnerability lies in the asynchronous timing behavior between client and server implementations during the SMC-R connection establishment process. During normal operation, the client and server engage in a multi-step handshake involving CLC (Connection Link Control) and LLC (Logical Link Control) confirmations, where the client sends a CLC proposal, receives an accept, and then sends a confirm. However, when the LLC confirm fails and times out, the server sends a decline message to the client. The problem occurs when the client's timeout period is insufficient compared to the server's timeout, creating a race condition where decline messages from the server are processed by the client's TCP connection that has already fallen back to a standard TCP connection. This timing discrepancy causes the decline message to be read from the TCP connection instead of the intended SMC connection, leading to data corruption and protocol errors. This issue directly relates to CWE-362 Concurrency Issues and CWE-691 Insufficient Control Flow Management, as it involves improper synchronization between concurrent connection handling processes and inadequate flow control during protocol state transitions.
The operational impact of CVE-2023-52775 extends beyond simple application errors to potentially compromise entire system reliability in high-performance computing environments. Applications using SMC-R for communication, particularly those in database systems like Redis, may experience intermittent connection failures, data corruption, and complete service disruption. The low probability of occurrence makes this vulnerability particularly dangerous as it may go undetected during normal operations but can cause catastrophic failures when triggered. The vulnerability affects systems that rely on SMC-R for low-latency communication between processes, including high-frequency trading systems, real-time data processing platforms, and distributed database clusters. From an ATT&CK perspective, this vulnerability maps to T1070.006 Indicator Removal on Host and T1566.001 Phishing: Spearphishing Attachment, as it can be exploited to create false data conditions that mask underlying communication failures, and T1595.001 Network Denial of Service, as the corruption can lead to complete service unavailability. The vulnerability is particularly concerning because it requires immediate attention due to the complexity of protocol-level fixes and the long-term implications for system stability.
The proposed fix for CVE-2023-52775 involves doubling the client timeout value to twice the server's timeout duration, effectively eliminating the race condition that causes decline messages to cross or collide during the confirm link timeout period. This simple yet effective change addresses the core timing issue by ensuring that client and server timeouts are properly synchronized, preventing the scenario where decline messages are processed through the fallback TCP connection. The patch implementation requires minimal code changes and maintains backward compatibility while resolving the fundamental timing conflict. Organizations should prioritize applying this patch immediately, especially in production environments where SMC-R is actively used for critical communications. System administrators should monitor affected applications for any residual issues following patch deployment and consider implementing additional monitoring for SMC-R connection states to detect similar timing-related issues. The fix aligns with security best practices for protocol implementation and demonstrates the importance of proper timeout management in distributed systems, particularly when dealing with complex multi-step handshake protocols that require precise timing coordination between communicating parties.