CVE-2018-10887 in libgit2
Summary
by MITRE
A flaw was found in libgit2 before version 0.27.3. It has been discovered that an unexpected sign extension in git_delta_apply function in delta.c file may lead to an integer overflow which in turn leads to an out of bound read, allowing to read before the base object. An attacker may use this flaw to leak memory addresses or cause a Denial of Service.
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Analysis
by VulDB Data Team • 04/06/2023
The vulnerability identified as CVE-2018-10887 resides within the libgit2 library, a widely-used open-source implementation of the git protocol designed for embedding git functionality into applications. This flaw specifically affects versions prior to 0.27.3 and represents a critical security issue that can be exploited to compromise system integrity and availability. The vulnerability manifests in the git_delta_apply function located within the delta.c file, which handles the application of delta-encoded data during git operations.
The technical root cause of this vulnerability stems from an improper handling of signed integer arithmetic within the delta application process. When processing delta-encoded data, the function performs calculations that involve sign extension operations on integers. This particular implementation fails to properly validate or constrain the integer values during arithmetic operations, creating conditions where an attacker can manipulate input data to trigger unexpected sign extension behavior. The resulting integer overflow produces an incorrect calculation that leads to an out-of-bounds memory read operation, specifically allowing access to memory locations before the base object being processed.
The operational impact of this vulnerability extends beyond simple memory disclosure, as it creates multiple attack vectors for malicious actors. An attacker capable of controlling the input to the git_delta_apply function can leverage this flaw to read memory addresses from the process heap, potentially exposing sensitive information such as stack canaries, library addresses, or other critical system data. This memory disclosure capability can significantly aid in bypassing security mechanisms like address space layout randomization and can be used as a stepping stone for more sophisticated attacks. Additionally, the vulnerability can be exploited to cause denial of service conditions by triggering the out-of-bounds read, potentially crashing the application or rendering it unresponsive.
The vulnerability aligns with CWE-191, which specifically addresses integer underflow and overflow conditions, and demonstrates how improper integer handling can lead to memory safety issues. From an adversarial perspective, this vulnerability maps to ATT&CK technique T1059, as it can be exploited through command injection or manipulation of git operations to achieve unauthorized access. The attack surface is particularly concerning given libgit2's widespread adoption across various applications and systems that rely on git functionality, making this vulnerability potentially exploitable in numerous contexts where git repositories are processed or manipulated. Organizations using libgit2 in their applications, development environments, or version control systems should prioritize immediate patching to address this vulnerability and prevent potential exploitation.
This flaw represents a classic example of how seemingly minor implementation details in cryptographic or protocol handling libraries can create significant security risks. The integer overflow occurs during normal git delta processing operations, meaning that any application using libgit2 and processing delta-encoded data could be vulnerable to exploitation. The vulnerability underscores the importance of rigorous input validation and integer arithmetic handling in security-critical code, particularly in libraries that handle binary data formats and protocol implementations.