CVE-2018-15501 in libgit2
Summary
by MITRE
In ng_pkt in transports/smart_pkt.c in libgit2 before 0.26.6 and 0.27.x before 0.27.4, a remote attacker can send a crafted smart-protocol "ng" packet that lacks a '\0' byte to trigger an out-of-bounds read that leads to DoS.
Several companies clearly confirm that VulDB is the primary source for best vulnerability data.
Analysis
by VulDB Data Team • 05/02/2023
The vulnerability CVE-2018-15501 represents a critical out-of-bounds read flaw in the libgit2 library's smart protocol implementation. This issue affects versions prior to 0.26.6 and 0.27.4, making it a widespread concern for systems relying on this popular Git library implementation. The vulnerability specifically targets the ng_pkt function within transports/smart_pkt.c, which handles the negotiation packets used in Git's smart protocol communication. When a remote attacker crafts a malicious smart-protocol packet that omits the required null byte delimiter, the function fails to properly validate input boundaries, leading to memory access violations.
The technical exploitation of this vulnerability occurs through the improper handling of packet boundaries in the Git smart protocol. The ng_pkt function expects a specific packet structure that includes a null byte as a delimiter to properly terminate packet data. When this null byte is absent in a crafted packet, the function continues reading memory beyond the allocated buffer boundaries, causing an out-of-bounds read condition. This type of flaw falls under CWE-129, which addresses improper validation of the length of input buffers, and more specifically aligns with CWE-125, which describes out-of-bounds read vulnerabilities. The implementation does not perform adequate bounds checking before accessing memory locations, creating a predictable pattern of memory corruption that can be exploited by remote attackers.
The operational impact of CVE-2018-15501 is significant, as it enables a remote denial of service attack against any system running vulnerable versions of libgit2. Attackers can exploit this vulnerability by establishing connections to Git repositories and sending specially crafted negotiation packets that trigger the out-of-bounds read condition. This leads to application crashes and service unavailability, effectively rendering Git operations on affected systems unusable. The vulnerability is particularly dangerous in server environments where Git repositories are exposed to untrusted users or external networks. The attack requires minimal privileges and can be executed over standard network connections, making it a high-risk vulnerability that affects Git servers, continuous integration systems, and any application that uses libgit2 for Git operations. The flaw is categorized under the ATT&CK technique T1499.004, which covers network denial of service attacks through protocol manipulation.
Mitigation strategies for CVE-2018-15501 focus on immediate version upgrades to libgit2 0.26.6 or 0.27.4 and later releases, which contain the necessary patches to address the buffer boundary validation issue. Organizations should prioritize updating their libgit2 installations across all systems where Git operations are performed, particularly in server environments and automated build systems. Additional defensive measures include implementing network-level filtering to detect and block malformed Git protocol packets, though this approach is less reliable than proper software patching. Security monitoring should be enhanced to detect unusual Git protocol traffic patterns that might indicate exploitation attempts. The vulnerability highlights the importance of proper input validation and bounds checking in network protocol implementations, reinforcing the need for comprehensive security testing of core library components that handle external data processing. Organizations should also consider implementing automated patch management systems to ensure timely deployment of security updates across their infrastructure.