CVE-2017-7869 in GnuTLS
Summary
by MITRE
GnuTLS before 2017-02-20 has an out-of-bounds write caused by an integer overflow and heap-based buffer overflow related to the cdk_pkt_read function in opencdk/read-packet.c. This issue (which is a subset of the vendor's GNUTLS-SA-2017-3 report) is fixed in 3.5.10.
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Analysis
by VulDB Data Team • 11/29/2022
The vulnerability identified as CVE-2017-7869 represents a critical security flaw in the GnuTLS cryptographic library that affects versions prior to 2017-02-20. This issue manifests as an out-of-bounds write condition that stems from an integer overflow and subsequent heap-based buffer overflow within the cdk_pkt_read function located in opencdk/read-packet.c. The flaw occurs during the processing of OpenCDK packet data structures, which are fundamental components used for handling cryptographic data in the library's operations. The vulnerability is particularly concerning because it allows for potential arbitrary code execution when malformed data is processed through the affected function.
The technical root cause of this vulnerability lies in improper input validation and memory management within the packet reading functionality. When the cdk_pkt_read function processes incoming data packets, it fails to adequately validate the size parameters of the incoming data, leading to an integer overflow condition. This overflow subsequently results in a heap-based buffer overflow where the application attempts to write data beyond the allocated memory boundaries. The issue is classified as a CWE-121 heap-based buffer overflow, which is a well-known category of memory corruption vulnerabilities that can be exploited to execute arbitrary code or cause denial of service conditions. The vulnerability affects the library's ability to properly parse and handle malformed packet data structures, creating a path for attackers to manipulate memory layout and potentially gain unauthorized access to system resources.
The operational impact of CVE-2017-7869 extends beyond simple denial of service scenarios, as it represents a potential attack vector for remote code execution. Systems utilizing vulnerable versions of GnuTLS for secure communications, including web servers, email servers, and other network services that rely on TLS/SSL encryption, could be compromised if they process untrusted data through the affected library. The vulnerability can be triggered through various attack vectors including processing of malformed certificates, encrypted communications with malicious peers, or manipulation of cryptographic data during transport. According to the vendor's security advisory GNUTLS-SA-2017-3, this issue specifically affects the OpenCDK component within GnuTLS, which handles OpenPGP packet structures and can be exploited when the library processes corrupted or specially crafted data. The vulnerability's exploitation potential aligns with ATT&CK technique T1059.007 for command and control communication and T1068 for local privilege escalation through memory corruption attacks.
Mitigation strategies for CVE-2017-7869 primarily involve immediate upgrading to GnuTLS version 3.5.10 or later, which contains the necessary patches to address both the integer overflow and buffer overflow conditions. Organizations should conduct comprehensive vulnerability assessments to identify all systems utilizing vulnerable GnuTLS versions, particularly those running web servers, email services, or any application that relies on TLS/SSL encryption for secure communications. Additional protective measures include implementing network segmentation to limit exposure, deploying intrusion detection systems to monitor for exploitation attempts, and establishing robust patch management procedures to ensure timely updates. Security teams should also consider implementing runtime protections such as address space layout randomization and stack canaries to reduce the effectiveness of potential exploitation attempts. The fix implemented in version 3.5.10 specifically addresses the integer overflow by adding proper bounds checking and input validation to prevent the overflow condition that led to the buffer overflow, thereby eliminating the out-of-bounds write vulnerability at its source.