CVE-2025-55113: BMC Control-M/Agent Auth Bypass Flaw

CVE-2025-55113 Overview

CVE-2025-55113 is a critical authentication bypass vulnerability affecting BMC Control-M/Agent software. The flaw exists in the Access Control List (ACL) enforcement mechanism when the C router is in use. Due to improper handling of NULL bytes in the email address field of client certificates, an attacker can craft a malicious certificate that causes the ACL verification process to terminate prematurely, effectively bypassing configured access controls.

This vulnerability represents a classic NULL byte injection issue (CWE-158) where string parsing stops at the first NULL character encountered, allowing attackers to manipulate certificate validation logic and gain unauthorized access to protected resources.

Critical Impact

Attackers can completely bypass Access Control List restrictions by exploiting NULL byte handling in client certificate email addresses, potentially gaining unauthorized access to Control-M/Agent managed systems.

Affected Products

• BMC Control-M/Agent versions 9.0.18 to 9.0.20 (out-of-support, C router is default)
• Potentially earlier unsupported Control-M/Agent versions
• Newer Control-M/Agent versions where the C router is manually enabled via JAVA_AR setting

Discovery Timeline

• September 16, 2025 - CVE-2025-55113 published to NVD
• October 10, 2025 - Last updated in NVD database

Technical Details for CVE-2025-55113

Vulnerability Analysis

The vulnerability stems from how the Control-M/Agent processes email address fields within X.509 client certificates during ACL enforcement. When the C router component is active, the verification routine uses string comparison functions that interpret NULL bytes (\\x00) as string terminators rather than treating them as part of the certificate data.

This allows an attacker to construct a certificate with an email address like admin@trusted-domain.com\\x00@attacker.com. When processed by the vulnerable ACL verification code, only the portion before the NULL byte (admin@trusted-domain.com) is evaluated, allowing the certificate to pass ACL checks even though it was issued to a different entity.

The C router is the default configuration in out-of-support versions 9.0.18 through 9.0.20, making legacy deployments particularly vulnerable. Newer versions can also be affected if administrators have explicitly configured the JAVA_AR setting to use the C router.

Root Cause

The root cause is improper neutralization of NULL bytes within input (CWE-158) in the certificate email address parsing logic. The C router component uses C-style string handling that treats NULL bytes as string terminators, rather than properly validating the entire certificate field as binary data. This creates a mismatch between how the certificate is issued and how it is validated.

Attack Vector

The attack requires network access to the Control-M/Agent service. An attacker would need to:

1. Obtain or generate a client certificate containing a specially crafted email address with an embedded NULL byte
2. Construct the email address so the portion before the NULL byte matches an allowed entry in the target ACL
3. Present this certificate during the TLS handshake when connecting to the Control-M/Agent
4. The vulnerable verification code processes only the portion before the NULL byte, granting access

This is a network-based attack that requires some complexity in crafting the malicious certificate, but requires no prior authentication or user interaction. Upon successful exploitation, an attacker gains the access privileges associated with the spoofed identity.

The vulnerability mechanism exploits the NULL byte termination behavior in string processing. When a certificate email field contains a sequence like legitimate-user@allowed-domain.com\\x00attacker-suffix, the ACL verification function interprets only legitimate-user@allowed-domain.com as the email address, terminating processing at the NULL byte. For detailed technical information, refer to the BMC Knowledge Article #000441967.

Detection Methods for CVE-2025-55113

Indicators of Compromise

• Client certificates containing NULL bytes (\\x00) in the email address or other subject fields
• Unusual certificate validation events where the processed email address differs from the full certificate data
• Connection attempts from certificates with suspicious dual-domain email patterns
• Authentication events where the logged identity doesn't match expected patterns

Detection Strategies

• Implement deep packet inspection to identify TLS client certificates with NULL bytes in subject fields
• Monitor Control-M/Agent authentication logs for discrepancies between expected and actual certificate identities
• Deploy certificate validation rules that reject certificates containing NULL bytes in email fields
• Configure SentinelOne to detect exploitation attempts targeting certificate validation bypass patterns

Monitoring Recommendations

• Enable verbose logging on Control-M/Agent to capture full certificate details during authentication
• Set up alerts for authentication events from unexpected certificate subjects or issuers
• Monitor for connections from systems that don't match your certificate provisioning infrastructure
• Review Access Control List match events against expected authorized entities

How to Mitigate CVE-2025-55113

Immediate Actions Required

• Upgrade Control-M/Agent to a supported version with the security fix applied
• If using out-of-support versions (9.0.18-9.0.20), plan emergency migration to supported releases
• Review and restrict which certificate authorities are trusted by Control-M/Agent
• Audit current ACL configurations and monitor for unauthorized access attempts
• Consider disabling the C router in favor of the Java router where possible via JAVA_AR configuration

Patch Information

BMC has released security updates to address this vulnerability. Refer to BMC Knowledge Article #000441967 and BMC Knowledge Article #000442099 for detailed patching instructions and supported version information.

Workarounds

• Switch from the C router to the Java router by configuring the JAVA_AR setting appropriately
• Implement network segmentation to limit which systems can connect to Control-M/Agent services
• Deploy additional network-level access controls (firewalls, VPNs) as a defense-in-depth measure
• Use certificate pinning or stricter CA validation to limit accepted certificates

# Configuration example - Switch to Java router to avoid vulnerable C router
# Edit Control-M/Agent configuration file
# Set JAVA_AR parameter to enable Java-based authentication router
JAVA_AR=Y

# Restart Control-M/Agent service after configuration change
# Consult BMC documentation for your specific platform