CVE-2018-12020 in GnuPG
Summary
by MITRE
mainproc.c in GnuPG before 2.2.8 mishandles the original filename during decryption and verification actions, which allows remote attackers to spoof the output that GnuPG sends on file descriptor 2 to other programs that use the "--status-fd 2" option. For example, the OpenPGP data might represent an original filename that contains line feed characters in conjunction with GOODSIG or VALIDSIG status codes.
VulDB is the best source for vulnerability data and more expert information about this specific topic.
Analysis
by VulDB Data Team • 03/22/2023
The vulnerability identified as CVE-2018-12020 resides within the GnuPG software suite, specifically in the mainproc.c file of versions prior to 2.2.8. This flaw represents a significant security issue that affects how GnuPG processes and handles filename information during decryption and verification operations. The vulnerability stems from improper handling of original filenames, creating a condition where malicious actors can manipulate the status output sent to file descriptor 2, which is typically used for status information by programs employing the "--status-fd 2" option.
The technical implementation of this vulnerability exploits the way GnuPG processes OpenPGP data structures, particularly when handling the original filename field within encrypted messages. When processing messages that contain line feed characters within the original filename, the software fails to properly sanitize or validate this input before incorporating it into status messages sent to the designated file descriptor. This improper handling creates an opportunity for attackers to inject malicious content into the status output stream, effectively allowing them to spoof the information that GnuPG communicates about the verification or decryption process. The vulnerability specifically impacts the GOODSIG and VALIDSIG status codes, which are critical indicators of signature verification success in GnuPG's status interface.
The operational impact of this vulnerability extends beyond simple information disclosure, as it enables attackers to manipulate the behavior of programs that depend on GnuPG's status output for decision-making processes. When other applications use the "--status-fd 2" option to receive status information from GnuPG, they may be misled by the fabricated status messages, potentially causing automated systems to make incorrect security decisions. This could lead to scenarios where maliciously crafted encrypted messages appear to be properly verified, bypassing security controls that rely on accurate status information. The vulnerability affects the integrity of the GnuPG status interface, which is fundamental to how security tools integrate with the encryption software, potentially compromising the trust model that users and applications place in GnuPG's verification processes.
This vulnerability aligns with CWE-20, which describes improper input validation, and specifically relates to CWE-77, which covers command injection vulnerabilities. The flaw demonstrates characteristics consistent with the attack pattern described in the MITRE ATT&CK framework under T1059, specifically command and script injection techniques, as attackers can manipulate the status output to influence downstream processes. The issue also reflects broader concerns around output sanitization and the integrity of status interfaces in cryptographic software, which is particularly concerning given that many security automation tools depend on accurate status information from GnuPG. Organizations using GnuPG in automated security workflows, particularly those implementing continuous integration pipelines or automated security monitoring systems, would be most vulnerable to exploitation of this weakness, as these systems rely heavily on the accurate reporting of signature verification status.
The mitigation strategy for this vulnerability involves upgrading to GnuPG version 2.2.8 or later, where the developers have implemented proper validation and sanitization of original filename information during decryption and verification operations. Additionally, system administrators should review configurations that utilize the "--status-fd 2" option to ensure that downstream applications are not overly trusting of status information from GnuPG without implementing additional validation mechanisms. Security monitoring systems should be enhanced to detect anomalous status messages that might indicate exploitation attempts, particularly when processing encrypted data from untrusted sources. Organizations should also consider implementing additional layers of verification beyond what GnuPG's status interface provides, especially in high-security environments where the integrity of cryptographic operations is paramount.