CVE-2018-0739 in Fujitsu M10-1
Summary
by MITRE
Constructed ASN.1 types with a recursive definition (such as can be found in PKCS7) could eventually exceed the stack given malicious input with excessive recursion. This could result in a Denial Of Service attack. There are no such structures used within SSL/TLS that come from untrusted sources so this is considered safe. Fixed in OpenSSL 1.1.0h (Affected 1.1.0-1.1.0g). Fixed in OpenSSL 1.0.2o (Affected 1.0.2b-1.0.2n).
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Analysis
by VulDB Data Team • 05/03/2025
The vulnerability described in CVE-2018-0739 represents a classic stack-based buffer overflow scenario that arises from improper handling of recursive data structures within the OpenSSL cryptographic library. This issue specifically affects the ASN.1 parsing functionality where maliciously constructed data structures with recursive definitions can cause excessive stack consumption during processing. The vulnerability manifests when OpenSSL encounters PKCS7 structures that contain recursive type definitions, which can lead to deep recursive calls that eventually exhaust the available stack space. This particular flaw demonstrates the critical importance of input validation and proper resource management when processing structured data formats that may contain self-referential elements.
The technical implementation of this vulnerability stems from the way OpenSSL's ASN.1 parser handles recursive type definitions without adequate stack depth monitoring or recursion limits. When processing malicious input containing deeply nested recursive structures, the parser performs recursive function calls that consume stack space proportional to the depth of recursion present in the input data. This recursive descent continues until the stack overflow occurs, causing the application to crash and resulting in a denial of service condition. The vulnerability is particularly dangerous because it can be triggered through untrusted input sources such as SSL/TLS handshakes or certificate processing, making it exploitable in network-based attacks. According to CWE classification, this vulnerability maps to CWE-674, which describes "Uncontrolled Recursion" and falls under the broader category of software weaknesses related to improper handling of recursive data structures.
The operational impact of CVE-2018-0739 extends beyond simple denial of service conditions as it represents a potential vector for more sophisticated attacks that could be combined with other vulnerabilities. While the vulnerability is not considered directly exploitable for remote code execution in SSL/TLS contexts due to the lack of untrusted input sources within the TLS protocol itself, it still poses significant risks to applications that process external PKCS7 data structures. The fix implemented by OpenSSL in versions 1.1.0h and 1.0.2o involved adding stack depth checks and recursion limiting mechanisms to prevent excessive stack consumption during ASN.1 parsing operations. These mitigations align with ATT&CK technique T1499.004, which covers "File System Wipe" through resource exhaustion, and demonstrate the importance of implementing proper recursion guards in cryptographic libraries. Organizations running affected OpenSSL versions must prioritize updating to patched releases to prevent potential denial of service attacks that could impact availability of critical services.
The vulnerability highlights fundamental security considerations in cryptographic library design and the importance of robust input validation. Modern security practices emphasize the need for defensive programming techniques that prevent resource exhaustion attacks, particularly in libraries that handle untrusted data. The fix implemented by OpenSSL demonstrates proper remediation through stack depth monitoring and recursion limiting, which are standard defensive measures against such vulnerabilities. This case study reinforces the principle that cryptographic libraries must be designed with proper resource management in mind, as these components often process data from multiple sources and must be resilient against malicious inputs. The vulnerability also underscores the importance of comprehensive testing of data parsing routines with recursive structures and the necessity of implementing appropriate safeguards to prevent stack-based buffer overflows in production cryptographic implementations. Organizations should consider implementing additional monitoring and alerting mechanisms to detect potential exploitation attempts and ensure that all systems using OpenSSL are regularly updated with the latest security patches.