CVE-2025-62507

Executive Summary

CVE-2025-62507 is a critical stack buffer overflow vulnerability in Redis, an open-source in-memory database. The flaw exists in versions 8.2.0 through 8.2.2 and is triggered by the XACKDEL command when a user provides multiple IDs. This overflow can potentially lead to remote code execution (RCE), allowing an attacker to compromise the Redis server. The vulnerability has been patched in version 8.2.3. As a workaround, administrators can restrict access to the XACKDEL command using Redis ACLs. No public proof-of-concept (PoC) or exploit code is currently available, and the EPSS score is 0.0%, indicating low exploitation activity at this time.

CVSS Breakdown & Threat Level

The CVSS score is listed as 0.0, which is likely a placeholder. Based on the vulnerability type (stack buffer overflow leading to potential RCE), a reasonable CVSS v3.1 vector would be:

• Attack Vector (AV): Network (N) – The command can be sent over the network.
• Attack Complexity (AC): Low (L) – No special conditions are required.
• Privileges Required (PR): Low (L) – An attacker needs a valid Redis user account with permission to execute XACKDEL.
• User Interaction (UI): None (N) – No user interaction is required.
• Scope (S): Unchanged (U) – The vulnerability affects the Redis process itself.
• Confidentiality (C): High (H) – Potential for arbitrary code execution could lead to data exfiltration.
• Integrity (I): High (H) – Code execution allows modification of data.
• Availability (A): High (H) – Code execution could crash the service or be used for denial of service.

Estimated CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H Estimated Base Score: 8.8 (High)

Threat Level: High. Although no public exploit exists, the vulnerability is in a widely used data store, and the potential for RCE makes it a high-priority target for threat actors.

Deep Dive & Mechanics

The vulnerability resides in the XACKDEL command, which is used to acknowledge and delete stream entries. The command accepts a stream key followed by one or more entry IDs. The flaw occurs in the parsing and processing of these IDs.

Root Cause: A stack buffer overflow occurs when the XACKDEL command processes multiple IDs. The code likely allocates a fixed-size buffer on the stack to store or process the IDs. When more IDs are provided than the buffer can hold, the overflow corrupts adjacent stack memory, including the return address and other critical data.

Trigger: An attacker with a valid Redis connection and permission to execute XACKDEL can send a command with a large number of IDs (e.g., XACKDEL mystream id1 id2 id3 ... idN). The exact number required to trigger the overflow depends on the buffer size and the length of each ID.

Impact: Successful exploitation can overwrite the return address, allowing an attacker to redirect execution to arbitrary code (shellcode). This leads to full remote code execution on the Redis server, potentially compromising the entire host.

Vulnerable vs. Patched Code

The vulnerable code is in the xackdelCommand function within src/t_stream.c. The patched version (8.2.3) introduces bounds checking and proper validation of the number of IDs.

Vulnerable Code (Conceptual):

void xackdelCommand(client *c) {
    // ... setup ...
    char buffer[256]; // Fixed-size stack buffer
    int offset = 0;
    for (int j = 2; j < c->argc; j++) {
        // No bounds check on offset
        offset += snprintf(buffer + offset, sizeof(buffer) - offset, "%s", c->argv[j]->ptr);
        // ... process ...
    }
    // ... overflow occurs if offset > 256 ...
}

Patched Code (Conceptual):

void xackdelCommand(client *c) {
    // ... setup ...
    // Limit the number of IDs to a safe maximum
    if (c->argc - 2 > MAX_XACKDEL_IDS) {
        addReplyError(c, "Too many IDs for XACKDEL");
        return;
    }
    char buffer[256];
    int offset = 0;
    for (int j = 2; j < c->argc; j++) {
        // Check remaining space before writing
        int needed = strlen(c->argv[j]->ptr) + 1;
        if (offset + needed > sizeof(buffer)) {
            addReplyError(c, "ID too long");
            return;
        }
        offset += snprintf(buffer + offset, sizeof(buffer) - offset, "%s", c->argv[j]->ptr);
        // ... process ...
    }
}

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• A Redis server running version 8.2.0 to 8.2.2.
• A valid Redis user account with permission to execute the XACKDEL command.
• Network access to the Redis port (default 6379).

Lab Setup:

1. Deploy a vulnerable Redis instance using Docker:

   docker run -d --name redis-vuln -p 6379:6379 redis:8.2.0
   

2. Connect to the Redis server using redis-cli:

   redis-cli -h 127.0.0.1 -p 6379
   

3. Authenticate if required:

   AUTH yourpassword
   

Exploitation Steps:

1. Create a stream to work with:

   XADD mystream * field1 value1
   

2. Craft a malicious XACKDEL command with a large number of IDs to trigger the overflow. The exact payload depends on the buffer size and the target architecture. A generic example:

   XACKDEL mystream $(python3 -c "print(' '.join(['A'*100]*100))")
   

   This sends 100 IDs, each 100 characters long, which may overflow the stack buffer.
3. If the overflow is successful, the Redis server may crash or allow code execution. For a full RCE, an attacker would need to craft a payload that overwrites the return address with a pointer to shellcode.

Note: No public exploit code is available. The above is a conceptual approach.

Blue Team (Defense & Detection)

Detection:

• Monitor for unusually long XACKDEL commands in Redis logs.
• Use network monitoring to detect large payloads sent to port 6379.
• Implement Redis ACLs to restrict XACKDEL to trusted users only.

Mitigation:

• Upgrade to Redis 8.2.3 or later.
• If upgrading is not possible, use ACLs to deny XACKDEL for all users except administrators:

  ACL SETUSER default -XACKDEL
  

• Monitor for crashes or unexpected behavior in Redis processes.

Indicators of Compromise (IOCs)

• Network IOCs:
  • Unusually large XACKDEL commands in Redis traffic (e.g., payloads > 1KB).
  • Repeated XACKDEL commands from the same source IP.
• Host IOCs:
  • Redis server crashes or segmentation faults.
  • Unexpected child processes spawned by the Redis process.
  • Modified Redis binaries or configuration files.
• Log IOCs:
  • Redis log entries showing XACKDEL with an excessive number of IDs.
  • System logs showing redis-server segfaults.

Detection Engineering

YARA Rule

rule CVE_2025_62507_Redis_XACKDEL_Overflow {
    meta:
        description = "Detects potential exploitation of CVE-2025-62507 in Redis XACKDEL command"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2025-62507"
    strings:
        $xackdel = "XACKDEL" nocase
        $long_id = /[A-Za-z0-9]{100,}/  // IDs longer than 100 characters
    condition:
        $xackdel and #long_id > 10
}

Sigma Rule

title: Redis XACKDEL Stack Buffer Overflow Attempt
id: 8f4a2b1c-3d5e-4f7a-8b9c-0d1e2f3a4b5c
status: experimental
description: Detects attempts to exploit CVE-2025-62507 by sending a large number of IDs in XACKDEL command
author: Valters IT
date: 2025-04-10
logsource:
    category: application
    product: redis
detection:
    selection:
        command: "XACKDEL"
        arg_count: "> 50"  # Adjust based on normal usage
    condition: selection
falsepositives:
    - Legitimate use of XACKDEL with many IDs (unlikely)
level: high

Suricata Rule

alert tcp $EXTERNAL_NET any -> $HOME_NET 6379 (msg:"CVE-2025-62507 Redis XACKDEL Stack Buffer Overflow Attempt"; flow:to_server,established; content:"XACKDEL"; nocase; pcre:"/XACKDEL\s+\S+(\s+\S+){50,}/"; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Upgrade Redis: Update to version 8.2.3 or later. This is the only complete fix.

   # For Docker
   docker pull redis:8.2.3
   docker stop redis-vuln
   docker run -d --name redis-patched -p 6379:6379 redis:8.2.3
   

2. Apply ACL Workaround: If upgrading is not possible, restrict the XACKDEL command:

   ACL SETUSER default -XACKDEL
   ACL SETUSER admin +XACKDEL
   

3. Network Segmentation: Limit access to Redis servers to trusted IPs only using firewalls or security groups.

Long-Term Measures:

• Implement regular vulnerability scanning for Redis instances.
• Monitor for new CVEs and apply patches promptly.
• Use Redis ACLs to enforce least privilege for all users.

Valters IT Signature: This report was generated by Valters IT Cyber Threat Intelligence Division. For questions, contact threatintel@valters.it.