CVE-2026-25506: MUNGE Buffer Overflow Vulnerability

CVE-2026-25506 Overview

CVE-2026-25506 is a buffer overflow vulnerability (CWE-787: Out-of-bounds Write) affecting the MUNGE authentication service, specifically within the munged daemon responsible for creating and validating user credentials. This vulnerability allows a local attacker to exploit improper bounds checking in message parsing to leak cryptographic key material from process memory, enabling the forgery of arbitrary MUNGE credentials to impersonate any user—including root—to services that rely on MUNGE for authentication.

Critical Impact

Local attackers can extract MAC subkeys used for credential verification, enabling complete authentication bypass and user impersonation across all MUNGE-protected services in HPC clusters and distributed computing environments.

Affected Products

• MUNGE versions 0.5 through 0.5.17
• Debian-based systems with vulnerable MUNGE packages
• HPC clusters and distributed computing environments using MUNGE authentication

Discovery Timeline

• February 10, 2026 - CVE-2026-25506 published to NVD
• February 10, 2026 - Last updated in NVD database

Technical Details for CVE-2026-25506

Vulnerability Analysis

The vulnerability exists in MUNGE's message unpacking routines within src/libcommon/m_msg.c. When the munged daemon processes incoming authentication messages, it unpacks various fields including an address length field (m->addr_len). Prior to the patch, there was no validation that the unpacked address length was within acceptable bounds before copying address data into a fixed-size buffer (m->addr).

A local attacker can craft a malicious message containing an oversized address length value. When munged attempts to copy the address data using this inflated length, it writes beyond the bounds of the destination buffer, corrupting adjacent memory structures. This memory corruption can be leveraged to leak the MAC subkey used internally for MUNGE credential verification.

Once the attacker obtains this cryptographic material, they can forge valid MUNGE credentials for any user on the system, including privileged accounts like root. Since MUNGE is commonly used for authentication in HPC clusters (e.g., with SLURM job schedulers), this vulnerability could allow unauthorized job submission, access to sensitive compute resources, and lateral movement across cluster nodes.

Root Cause

The root cause is missing input validation on the m->addr_len field before it is used to control a memory copy operation. The code trusted the user-supplied length value without verifying it against the maximum size of the destination buffer (sizeof(m->addr)), creating a classic buffer overflow condition.

Attack Vector

The attack requires local access to the system running munged. The attacker sends a specially crafted message to the MUNGE daemon with an oversized address length field, triggering the buffer overflow. The attack complexity is high as it requires precise memory manipulation to extract the cryptographic key material without crashing the daemon. However, successful exploitation allows complete compromise of the MUNGE authentication mechanism.

             else if ( _copy (m->realm_str, p, m->realm_len, p, q, &p) < 0) ;
             else if (!_unpack (&(m->ttl), &p, sizeof (m->ttl), q)) ;
             else if (!_unpack (&(m->addr_len), &p, sizeof (m->addr_len), q)) ;
+            else if (m->addr_len > sizeof (m->addr)) goto err;
             else if ( _copy (&(m->addr), p, m->addr_len, p, q, &p) < 0) ;
             else if (!_unpack (&(m->time0), &p, sizeof (m->time0), q)) ;
             else if (!_unpack (&(m->time1), &p, sizeof (m->time1), q)) ;

Source: GitHub Commit Update

The patch adds a bounds check ensuring m->addr_len does not exceed the size of the m->addr buffer before proceeding with the copy operation.

Detection Methods for CVE-2026-25506

Indicators of Compromise

• Unexpected crashes or restarts of the munged daemon process
• Unusual authentication activity from users who should not have access to specific resources
• Anomalous MUNGE credential creation patterns in system logs
• Memory corruption signatures in munged crash dumps or core files

Detection Strategies

• Monitor munged daemon logs for authentication anomalies or unexpected credential validations
• Implement memory protection monitoring to detect buffer overflow attempts against the munged process
• Deploy endpoint detection solutions capable of identifying exploitation of CWE-787 vulnerabilities
• Audit MUNGE-protected services for unexpected user access patterns

Monitoring Recommendations

• Enable verbose logging in MUNGE configuration to capture credential validation events
• Set up alerts for munged process crashes or unexpected restarts
• Monitor system call activity around the munged daemon for signs of exploitation attempts
• Implement file integrity monitoring on MUNGE configuration and key files

How to Mitigate CVE-2026-25506

Immediate Actions Required

• Upgrade MUNGE to version 0.5.18 or later immediately
• Regenerate MUNGE cryptographic keys after upgrading to ensure any potentially leaked key material is invalidated
• Restrict local access to systems running munged to trusted users only
• Review authentication logs for any signs of compromise prior to patching

Patch Information

The vulnerability is fixed in MUNGE version 0.5.18. The patch adds proper bounds checking to validate that the address length field does not exceed the buffer size before performing the memory copy operation. Security patches and updated packages are available through the following resources:

• MUNGE 0.5.18 Release
• Security Fix Commit
• GitHub Security Advisory GHSA-r9cr-jf4v-75gh
• Debian LTS Security Advisory

Workarounds

• Limit local shell access to systems running munged to only essential administrators
• Implement additional network segmentation around HPC cluster management nodes
• Monitor for suspicious local authentication activity while awaiting patch deployment
• Consider temporarily isolating critical MUNGE-protected services if patching cannot be performed immediately

# Verify MUNGE version and upgrade
munge --version
# If version is below 0.5.18, upgrade immediately

# For Debian/Ubuntu systems
sudo apt update && sudo apt install munge

# Regenerate MUNGE key after upgrade (run on head node)
sudo mungekey --force

# Restart the MUNGE daemon
sudo systemctl restart munge

# Verify the service is running with the patched version
sudo systemctl status munge
munge --version