Overview
In a recent discovery, a critical vulnerability, CVE-2025-55398, was identified in the mouse07410 asn1c through 0.9.29, a fork of vlm asn1c. This vulnerability may affect a range of applications and services using this version of asn1c for encoding and decoding ASN.1 data structures. ASN.1 (Abstract Syntax Notation One) is widely used in telecommunications and computer networking, and thus the vulnerability potentially has a broad impact.
The issue lies in the UPER (Unaligned Packed Encoding Rules), where asn1c-generated decoders fail to enforce INTEGER constraints when the bound is positive and exceeds 32 bits in length. This could potentially allow incorrect or malicious input to be processed, leading to serious consequences like system compromise or data leakage.
Vulnerability Summary
CVE ID: CVE-2025-55398
Severity: Critical (9.8 – CVSS Severity Score)
Attack Vector: Direct (via malformed ASN.1 data)
Privileges Required: None
User Interaction: None
Impact: System compromise, Data leakage
Affected Products
Product | Affected Versions
mouse07410 asn1c | 0.9.29 and earlier versions
How the Exploit Works
The vulnerability resides in the UPER (Unaligned Packed Encoding Rules) portion of the asn1c. UPER is used for efficient encoding and decoding of ASN.1 data structures. However, when it comes to handling INTEGER constraints that exceed 32 bits in length, asn1c-generated decoders fail to enforce these constraints.
This lack of constraint enforcement allows an attacker to send malformed ASN.1 data that can bypass the checks. This can lead to unexpected behavior or even allow malicious payload execution, depending on the application’s handling of decoded data.
Conceptual Example Code
While the specific exploitation would depend on the application using asn1c, a conceptual example might be similar to the following pseudocode:
# Pseudo-code for exploiting the vulnerability
def exploit(target_system):
malformed_asn1_data = generate_malformed_asn1_data() # A function to generate malformed ASN.1 data
response = target_system.decode(malformed_asn1_data) # The system would fail to enforce INTEGER constraints
if response.status == 'Success':
# If the malformed data is processed successfully, it indicates the system is vulnerable
print("System is vulnerable")
else:
print("Exploit failed")In this pseudo-code, generate_malformed_asn1_data is a function that would create an ASN.1 data structure with an INTEGER constraint that exceeds 32 bits in length. The decode function is used to process the data, and if the system fails to enforce the INTEGER constraint, it would process the malformed data, indicating the system is vulnerable.
