CVE-2015-1790 in OpenSSL
Summary
by MITRE
The PKCS7_dataDecodefunction in crypto/pkcs7/pk7_doit.c in OpenSSL before 0.9.8zg, 1.0.0 before 1.0.0s, 1.0.1 before 1.0.1n, and 1.0.2 before 1.0.2b allows remote attackers to cause a denial of service (NULL pointer dereference and application crash) via a PKCS#7 blob that uses ASN.1 encoding and lacks inner EncryptedContent data.
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Analysis
by VulDB Data Team • 05/21/2022
The vulnerability identified as CVE-2015-1790 represents a critical denial of service flaw within OpenSSL's PKCS#7 implementation that affects multiple version streams including 0.9.8, 1.0.0, 1.0.1, and 1.0.2 series. This issue stems from improper handling of PKCS#7 encoded data structures during the decryption process, specifically within the PKCS7_dataDecode function located in crypto/pkcs7/pk7_doit.c. The flaw manifests when processing ASN.1 encoded PKCS#7 blobs that lack the required inner EncryptedContent data, creating a scenario where the application encounters a NULL pointer dereference during normal operation. This vulnerability operates at the intersection of cryptographic protocol handling and memory management, making it particularly dangerous as it can be triggered through legitimate network traffic without requiring special privileges or authentication.
The technical exploitation of this vulnerability occurs when an attacker crafts a malicious PKCS#7 blob that conforms to ASN.1 encoding standards but omits the essential EncryptedContent field that PKCS#7 specifications require for proper decryption. When OpenSSL's PKCS7_dataDecode function attempts to process this malformed data structure, it fails to properly validate the presence of required components before attempting to dereference pointers to the missing EncryptedContent data. This results in a NULL pointer dereference that causes the application to crash and terminate unexpectedly, effectively providing a denial of service condition for any system processing such malformed data. The vulnerability aligns with CWE-476 which describes NULL pointer dereference conditions, and represents a classic example of inadequate input validation in cryptographic libraries where malformed data can cause application instability.
From an operational perspective, this vulnerability presents significant risks to systems that rely on OpenSSL for processing PKCS#7 encoded data, particularly those handling email encryption, code signing, or certificate management operations. The impact extends beyond simple service disruption as the vulnerability can affect web servers, email servers, and any application that processes PKCS#7 formatted data through OpenSSL libraries. Attackers can exploit this weakness by sending specially crafted PKCS#7 messages that trigger the crash condition, potentially leading to service unavailability for legitimate users. The vulnerability is particularly concerning because it can be triggered through normal network operations without requiring authentication, making it a low-effort, high-impact attack vector that can be easily automated against vulnerable systems.
The remediation strategy for CVE-2015-1790 involves immediate patching of affected OpenSSL versions to the latest stable releases that contain the necessary code modifications to properly validate PKCS#7 data structures before attempting decryption operations. Organizations should prioritize updating their OpenSSL installations across all systems that process PKCS#7 encoded data, including web servers, email systems, and any cryptographic applications. Additionally, network monitoring should be enhanced to detect unusual patterns of PKCS#7 data processing that might indicate exploitation attempts. The fix implemented by OpenSSL developers includes enhanced input validation that checks for the presence of required EncryptedContent fields before proceeding with decryption operations, preventing the NULL pointer dereference condition. This vulnerability serves as a reminder of the importance of robust input validation in cryptographic libraries and aligns with ATT&CK technique T1499.004 which covers network denial of service attacks, demonstrating how improper error handling in cryptographic libraries can create exploitable conditions that bypass traditional security controls.