CVE-2026-25243: 
Redis vulnerability analysis and mitigation

CVE-2026-25243 is a heap-based buffer overflow vulnerability in the Redis RESTORE command that can allow an authenticated attacker to trigger invalid memory access, potentially leading to remote code execution. It affects all versions of redis-server prior to 8.6.3 and was disclosed on May 5, 2026, by researchers Emil Lerner (discovered during the Wiz Zeroday Cloud event) and Joseph Surin. The vulnerability carries a CVSS v3.1 base score of 8.8 (High) and a CVSS v4.0 base score of 7.7 (High) (GitHub Advisory, Redis Release).

The root cause is insufficient validation of serialized values processed by the RESTORE command (CWE-122: Heap-based Buffer Overflow; CWE-20: Improper Input Validation). When a specially crafted serialized payload is supplied to RESTORE, the server fails to properly validate the input before processing it, resulting in unsafe heap memory accesses that can corrupt memory and potentially redirect execution flow. Exploitation requires network access to the Redis instance, valid credentials, and permission to execute the RESTORE command — making it a low-privilege, network-adjacent attack with no user interaction required (GitHub Advisory).

Successful exploitation can result in full compromise of the affected Redis server, including arbitrary code execution in the context of the Redis process, unauthorized access to all data stored in the instance (confidentiality impact), modification or deletion of data (integrity impact), and service disruption or crash (availability impact). Because Redis is frequently used as a shared cache or session store, a compromised instance may expose sensitive application data and could serve as a pivot point for lateral movement within internal networks (GitHub Advisory, Redis Release).

1. Reconnaissance: Identify Redis instances accessible over the network (default port 6379/TCP) using tools like Shodan, Censys, or nmap. Confirm the version is below 8.6.3.
2. Obtain credentials: Acquire valid Redis credentials (username/password) through credential stuffing, leaked configuration files, or exploitation of weak/default authentication settings.
3. Verify RESTORE permissions: Authenticate to the Redis instance using redis-cli -h <target> -p 6379 -a <password> and confirm the authenticated user has permission to execute the RESTORE command (not blocked by ACL rules).
4. Craft malicious payload: Construct a specially crafted serialized payload that exploits the insufficient validation in the RESTORE command handler to trigger a heap-based buffer overflow. The payload must be designed to corrupt heap memory in a controlled manner.
5. Execute RESTORE command: Send the crafted payload via the RESTORE command: RESTORE <key> 0 <malicious_serialized_payload>. The malformed input triggers invalid memory access in the Redis server process.
6. Achieve code execution: If the heap corruption is exploited successfully, arbitrary code executes in the context of the Redis server process, enabling reverse shell establishment, data exfiltration, or further lateral movement (GitHub Advisory).

• Network: Unexpected or anomalous connections to Redis port 6379/TCP from untrusted or external IP addresses; large or malformed RESTORE command payloads observed in network traffic captures.
• Logs: Redis server logs (redis.log) showing errors related to memory access violations, segmentation faults, or unexpected crashes following RESTORE command execution; repeated RESTORE commands from a single client with unusual payload sizes.
• Process: Redis server process spawning unexpected child processes (e.g., shells, curl, wget); abnormal CPU or memory usage spikes in the Redis process following RESTORE command activity.
• File System: Unexpected files written to the filesystem by the Redis process user; new cron jobs, scripts, or binaries created under directories writable by the Redis service account.

The primary remediation is to upgrade Redis to version 8.6.3 or later, which contains the fix for CVE-2026-25243 (Redis Release). As an immediate workaround without patching, administrators should restrict access to the RESTORE command using Redis ACL rules — for example: ACL SETUSER <username> nocommands +<allowed_commands> or explicitly blocking RESTORE with ACL SETUSER <username> -restore. Additionally, ensure Redis instances are not exposed to untrusted networks, enforce strong authentication, and apply the principle of least privilege to Redis user accounts (GitHub Advisory). Downstream distributions including Valkey, SUSE, openSUSE, Fedora, Amazon Linux 2023, and Red Hat have also released updated packages addressing this vulnerability.

The Redis security team published a combined advisory covering CVE-2026-25243 alongside four other CVEs patched in version 8.6.3, describing the release urgency as "SECURITY" (Redis Blog). Security news outlets including GBHackers, CyberSecurityNews, and The Hacker News covered the Redis vulnerability batch, with headlines emphasizing RCE risk to Redis servers (GBHackers, CyberSecurityNews). The Canadian Centre for Cyber Security (CCCS) and Hong Kong CERT (HKCERT) issued advisories urging users to patch (CCCS Advisory, HKCERT). A technical deep-dive was published by Zeroday Cloud, the event at which the vulnerability was originally discovered (Zeroday Cloud).