CVE-2025-42940: SAP CommonCryptoLib DoS Vulnerability

CVE-2025-42940 Overview

CVE-2025-42940 is an out-of-bounds write vulnerability affecting SAP CommonCryptoLib, a critical cryptographic library used across SAP enterprise products. The vulnerability occurs during pre-authentication parsing of ASN.1 (Abstract Syntax Notation One) data received over the network. Due to insufficient boundary checks, specially crafted ASN.1 data can trigger memory corruption, leading to application crashes and denial of service conditions.

Critical Impact

This vulnerability allows unauthenticated remote attackers to crash SAP applications by sending malformed ASN.1 data, causing significant availability disruption to enterprise systems without requiring any user interaction or prior authentication.

Affected Products

• SAP CommonCryptoLib (specific versions detailed in SAP Note #3633049)
• SAP applications utilizing CommonCryptoLib for cryptographic operations
• SAP enterprise systems with network-exposed cryptographic endpoints

Discovery Timeline

• 2025-11-11 - CVE-2025-42940 published to NVD
• 2026-04-15 - Last updated in NVD database

Technical Details for CVE-2025-42940

Vulnerability Analysis

The vulnerability is classified as CWE-787 (Out-of-Bounds Write), indicating that SAP CommonCryptoLib writes data past the boundaries of allocated memory buffers during ASN.1 parsing operations. ASN.1 is a standard interface description language used extensively in cryptographic protocols for encoding data structures, including certificates, keys, and authentication tokens.

When CommonCryptoLib processes incoming ASN.1-encoded data during pre-authentication phases (such as TLS handshakes or certificate validation), it fails to properly validate length fields and structural boundaries. An attacker can exploit this by sending specially crafted ASN.1 data containing malformed length encodings or nested structures that exceed expected buffer sizes.

The attack can be conducted remotely over the network without any authentication requirements or user interaction. While the vulnerability does not allow data theft or system modification, the resulting memory corruption reliably crashes the affected application, creating a denial of service condition that can severely impact business operations.

Root Cause

The root cause is inadequate boundary validation in the ASN.1 parsing routines within SAP CommonCryptoLib. When processing length-prefixed data structures common in ASN.1 encoding (such as SEQUENCE, SET, OCTET STRING, and BIT STRING types), the library does not properly verify that declared lengths stay within allocated buffer boundaries before writing data.

This oversight allows attackers to specify length values that exceed buffer allocations, causing the parser to write beyond intended memory regions. The resulting memory corruption destabilizes the application state, typically leading to immediate process termination through segmentation faults or access violations.

Attack Vector

The attack is network-based and requires no authentication or user interaction. An attacker can target any SAP application that uses CommonCryptoLib for processing incoming cryptographic data. Common attack surfaces include:

The vulnerability can be exploited by sending malformed ASN.1 data during initial connection establishment phases, before any authentication occurs. This makes the attack particularly dangerous as it can disrupt services from completely external, unauthenticated positions. Potential attack scenarios include crafting malicious TLS ClientHello messages, certificate requests, or other ASN.1-encoded protocol messages that trigger the parsing flaw.

Detection Methods for CVE-2025-42940

Indicators of Compromise

• Unexpected SAP application crashes or service restarts, particularly those involving cryptographic operations
• Segmentation fault or access violation errors in application logs referencing CommonCryptoLib components
• Unusual volume of malformed connection attempts from external IP addresses
• Core dumps or crash logs showing memory corruption in ASN.1 parsing routines

Detection Strategies

• Monitor SAP application logs for sudden terminations or restart events without legitimate cause
• Implement network intrusion detection rules to identify malformed ASN.1 structures in incoming traffic
• Deploy application crash monitoring to detect repeated failures in CommonCryptoLib-dependent services
• Analyze network traffic for unusually large or malformed length fields in ASN.1-encoded data streams

Monitoring Recommendations

• Enable detailed crash logging and core dump analysis for SAP applications
• Configure network security appliances to alert on suspicious ASN.1 parsing anomalies
• Implement service availability monitoring with automated alerting for unexpected downtime
• Review firewall logs for repeated connection attempts from single sources targeting cryptographic endpoints

How to Mitigate CVE-2025-42940

Immediate Actions Required

• Apply the security patch detailed in SAP Note #3633049 immediately
• Prioritize patching for internet-facing SAP systems and applications
• Temporarily restrict network access to affected services from untrusted networks if immediate patching is not possible
• Implement network-level filtering to detect and block malformed ASN.1 traffic where feasible

Patch Information

SAP has released security patches addressing this vulnerability through SAP Note #3633049. Organizations should review the SAP Security Patch Day announcements for complete patch details and deployment guidance. The patch implements proper boundary validation in the ASN.1 parsing routines to prevent out-of-bounds memory writes.

Workarounds

• Restrict network access to SAP applications using CommonCryptoLib through firewall rules limiting connections to trusted sources only
• Deploy a Web Application Firewall (WAF) or network security appliance capable of inspecting and filtering malformed ASN.1 data
• Isolate affected SAP systems on network segments with strict access controls until patches can be applied
• Consider temporarily disabling non-essential network services that rely on CommonCryptoLib parsing

# Example: Restrict network access to SAP services (adapt ports as needed)
# Limit incoming connections to trusted IP ranges only
iptables -A INPUT -p tcp --dport 443 -s 10.0.0.0/8 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -s 172.16.0.0/12 -j ACCEPT
iptables -A INPUT -p tcp --dport 443 -j DROP