CVE-2025-49112: Valkey Integer Underflow Vulnerability

CVE-2025-49112 Overview

An integer underflow vulnerability exists in the setDeferredReply function within networking.c in Valkey through version 8.1.1. The vulnerability occurs in the calculation prev->size - prev->used, which can result in an integer underflow condition when the prev->used value exceeds prev->size. This type of arithmetic error can lead to unexpected behavior in memory operations and potentially cause denial of service conditions.

Critical Impact

This integer underflow vulnerability in Valkey's networking component could potentially cause memory corruption or service disruption in adjacent network scenarios, affecting the availability of key-value store operations.

Affected Products

• Valkey through version 8.1.1
• Redis (related codebase - see GitHub Redis Source Code)

Discovery Timeline

• 2025-06-02 - CVE-2025-49112 published to NVD
• 2025-06-02 - Last updated in NVD database

Technical Details for CVE-2025-49112

Vulnerability Analysis

This vulnerability is classified as CWE-191 (Integer Underflow). The flaw resides in the setDeferredReply function located in networking.c. When processing deferred replies in the networking layer, the code performs an arithmetic subtraction operation between prev->size and prev->used. If prev->used is greater than prev->size due to improper bounds checking or state corruption, the subtraction results in an integer underflow.

Integer underflow vulnerabilities occur when an arithmetic operation attempts to create a numeric value that is below the minimum representable value for the data type. In this case, the underflow could cause the resulting value to wrap around to a very large positive number, potentially leading to incorrect memory allocations, buffer overruns, or other memory safety issues.

The attack requires adjacent network access, meaning an attacker would need to be on the same local network segment as the vulnerable Valkey instance. While the complexity to exploit this vulnerability is high, it does not require any privileges or user interaction.

Root Cause

The root cause of this vulnerability is insufficient validation of the relationship between prev->size and prev->used before performing the subtraction operation. The code assumes that prev->size will always be greater than or equal to prev->used, but this invariant is not properly enforced. When this assumption is violated, the arithmetic operation produces an underflowed value that can propagate through subsequent memory operations.

The vulnerable code path can be examined in the Valkey source code at networking.c line 886.

Attack Vector

The vulnerability requires adjacent network access to exploit. An attacker positioned on the same network segment as the vulnerable Valkey server could potentially craft specific network requests designed to trigger the condition where prev->used exceeds prev->size. The attack complexity is high due to the specific conditions required to trigger the underflow, and successful exploitation would primarily impact availability through potential service crashes or resource exhaustion.

The vulnerability mechanism involves the deferred reply handling in Valkey's networking stack. When processing client connections and responses, the setDeferredReply function manages buffer state tracking. The integer underflow can occur when buffer state becomes inconsistent, potentially through malformed requests or race conditions in connection handling.

Detection Methods for CVE-2025-49112

Indicators of Compromise

• Unexpected crashes or restarts of Valkey server processes
• Memory allocation errors or segmentation faults in Valkey logs
• Anomalous network traffic patterns targeting Valkey ports from adjacent network hosts
• Unusually large memory allocations reported in server statistics

Detection Strategies

• Monitor Valkey server logs for crash dumps or error messages related to networking.c or memory operations
• Implement network monitoring to detect unusual connection patterns or malformed requests to Valkey instances
• Use memory profiling tools to detect abnormal allocation patterns that may indicate exploitation attempts
• Deploy runtime application self-protection (RASP) solutions to detect integer underflow conditions

Monitoring Recommendations

• Enable detailed logging for Valkey server operations and review for anomalies
• Monitor system metrics including memory usage, process crashes, and restart frequency
• Implement network segmentation monitoring to track adjacent network access patterns
• Use SentinelOne's real-time monitoring capabilities to detect process anomalies and potential exploitation attempts

How to Mitigate CVE-2025-49112

Immediate Actions Required

• Update Valkey to a patched version when available (versions after 8.1.1)
• Review and apply the fix from Valkey Pull Request #2101
• Implement network segmentation to limit adjacent network access to Valkey instances
• Monitor Valkey deployments for signs of exploitation or instability

Patch Information

A fix has been submitted via GitHub Valkey Pull Request #2101. Organizations running Valkey through version 8.1.1 should monitor for official releases incorporating this fix and plan for immediate deployment once available. The patch addresses the integer underflow by adding proper bounds validation before performing the arithmetic operation.

Workarounds

• Restrict network access to Valkey instances to trusted hosts only using firewall rules
• Implement network segmentation to prevent adjacent network attackers from reaching Valkey services
• Deploy Valkey behind a reverse proxy or API gateway that can filter malicious requests
• Consider running Valkey in isolated network environments with strict access controls

# Configuration example - Restrict Valkey network access
# Add firewall rules to limit adjacent network access
iptables -A INPUT -p tcp --dport 6379 -s 10.0.0.0/24 -j ACCEPT
iptables -A INPUT -p tcp --dport 6379 -j DROP

# Configure Valkey bind address to limit network exposure
# In valkey.conf:
# bind 127.0.0.1 10.0.0.1
# protected-mode yes