CVE-2023-41056: Redis Integer Overflow RCE Vulnerability

CVE-2023-41056 Overview

CVE-2023-41056 is an integer overflow vulnerability in Redis, the popular in-memory database that persists data to disk. The vulnerability exists in how Redis handles the resizing of memory buffers. When processing certain operations that trigger buffer resizing, Redis incorrectly calculates the new buffer size, resulting in an integer overflow condition. This integer overflow subsequently leads to a heap overflow, which can potentially be exploited to achieve remote code execution on affected systems.

Critical Impact

This vulnerability can lead to remote code execution through heap overflow exploitation, potentially allowing attackers to compromise Redis servers and gain control of the underlying system.

Affected Products

• Redis versions prior to 7.0.15 (7.0.x branch)
• Redis versions prior to 7.2.4 (7.2.x branch)
• Fedora 38 and Fedora 39 (with vulnerable Redis packages)

Discovery Timeline

• 2024-01-10 - CVE-2023-41056 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2023-41056

Vulnerability Analysis

This vulnerability represents a classic memory safety issue where improper integer arithmetic leads to catastrophic memory corruption. When Redis needs to resize an internal memory buffer to accommodate growing data, it performs calculations to determine the new buffer size. However, under specific conditions, this calculation can overflow, wrapping around to a much smaller value than intended. This results in Redis allocating an undersized buffer while still attempting to write the full amount of data into it, causing a heap-based buffer overflow.

The attack requires network access and presents some exploitation complexity, as attackers must carefully craft requests that trigger the vulnerable code path with values that cause the integer overflow. However, no authentication is required, making internet-exposed Redis instances particularly vulnerable. Successful exploitation could allow attackers to execute arbitrary code with the privileges of the Redis process, potentially leading to complete system compromise, data theft, or use of the server in further attacks.

Root Cause

The root cause of CVE-2023-41056 is an integer overflow vulnerability (CWE-190) in Redis's memory buffer resizing logic. When computing new buffer sizes during dynamic resizing operations, the code fails to properly validate or check for integer overflow conditions before the allocation. This allows specially crafted inputs to cause the calculated size to wrap around, resulting in allocation of insufficient memory and subsequent heap corruption when the buffer is written to.

Attack Vector

The attack vector is network-based, meaning an attacker can exploit this vulnerability remotely without physical access to the target system. The attack complexity is considered high as successful exploitation requires:

1. Network Access: The attacker must be able to communicate with the Redis server over the network.
2. Trigger Conditions: Crafting specific requests that cause the memory buffer resize operation to encounter the integer overflow condition.
3. Heap Manipulation: Potentially arranging heap memory layout to achieve reliable code execution through the heap overflow.

Since Redis is commonly deployed as a backend data store and is sometimes exposed to untrusted networks, organizations should prioritize patching vulnerable instances immediately.

Detection Methods for CVE-2023-41056

Indicators of Compromise

• Unexpected Redis process crashes or memory corruption errors in Redis logs
• Anomalous memory allocation patterns or unusually high memory usage spikes in Redis processes
• Evidence of code execution or shell spawning from the Redis process context
• Suspicious network traffic patterns to Redis ports (typically 6379) with malformed or oversized commands

Detection Strategies

• Monitor Redis logs for segmentation faults, memory errors, or unexpected restarts that could indicate exploitation attempts
• Deploy network intrusion detection rules to identify malformed Redis protocol traffic or unusual command sequences
• Use memory protection tools and runtime application self-protection (RASP) to detect heap overflow conditions
• Implement Redis command auditing to track unusual or suspicious operations that could trigger buffer resizing

Monitoring Recommendations

• Enable Redis slow log and monitor for commands with unusual data sizes that could trigger buffer operations
• Configure system-level monitoring for Redis process memory usage and unexpected terminations
• Set up alerts for Redis service restarts or crashes that could indicate active exploitation
• Monitor network connections to Redis instances for connections from unexpected sources or geographic locations

How to Mitigate CVE-2023-41056

Immediate Actions Required

• Upgrade Redis to version 7.0.15 or later for the 7.0.x branch immediately
• Upgrade Redis to version 7.2.4 or later for the 7.2.x branch immediately
• Ensure Redis is not directly exposed to untrusted networks; use firewalls and network segmentation
• Enable Redis authentication and configure proper ACLs to limit access to trusted clients only

Patch Information

Redis has released patched versions that address this vulnerability. Organizations should upgrade to one of the following fixed versions:

• Redis 7.0.15 - Available via GitHub Redis Release 7.0.15
• Redis 7.2.4 - Available via GitHub Redis Release 7.2.4

Additional security details are available in the GitHub Security Advisory GHSA-xr47-pcmx-fq2m. Fedora users should apply the updated packages announced via the Fedora Package Announcements.

Workarounds

• Restrict network access to Redis using firewall rules to allow only trusted IP addresses
• Implement Redis authentication using the requirepass directive to prevent unauthorized access
• Deploy Redis behind a VPN or bastion host to prevent direct internet exposure
• Use Redis ACLs to restrict which commands can be executed and by which users

# Configuration example for Redis security hardening
# Add to redis.conf

# Require password authentication
requirepass your_strong_password_here

# Bind to localhost only if remote access is not required
bind 127.0.0.1 ::1

# Disable dangerous commands that could be abused
rename-command FLUSHALL ""
rename-command FLUSHDB ""
rename-command DEBUG ""

# Enable protected mode
protected-mode yes