CVE-2020-15904 in bsdiff4
Summary
by MITRE
A buffer overflow in the patching routine of bsdiff4 before 1.2.0 allows an attacker to write to heap memory (beyond allocated bounds) via a crafted patch file.
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Analysis
by VulDB Data Team • 07/23/2020
The vulnerability identified as CVE-2020-15904 represents a critical buffer overflow condition within the bsdiff4 library's patching functionality. This issue affects versions prior to 1.2.0 and specifically targets the heap memory management during patch application processes. The flaw manifests when the library processes maliciously crafted patch files that contain oversized data structures or malformed headers, leading to unauthorized memory writes beyond the allocated buffer boundaries. The vulnerability resides in the core patching routine that handles binary differences and applies them to target files, making it a fundamental security weakness in the library's memory handling mechanisms.
The technical implementation of this buffer overflow stems from inadequate bounds checking during the patch application phase. When bsdiff4 encounters a patch file, it reads header information and allocates memory buffers based on expected data sizes. However, the library fails to validate the actual size of incoming patch data against the allocated buffer dimensions, allowing attackers to craft patch files that exceed memory boundaries. This condition creates a classic heap-based buffer overflow scenario where arbitrary data can be written to adjacent memory locations, potentially corrupting program state or enabling code execution. The vulnerability operates at the intersection of memory management and input validation, with the flaw classified as a CWE-121 heap-based buffer overflow according to the Common Weakness Enumeration standards.
From an operational perspective, this vulnerability presents significant risks to systems that rely on bsdiff4 for binary patching operations. Attackers can exploit this weakness by preparing specially crafted patch files that, when processed by vulnerable applications, trigger the buffer overflow condition. The impact extends beyond simple memory corruption as it can lead to remote code execution, denial of service conditions, or information disclosure depending on how the vulnerable system handles the corrupted memory state. The attack vector is particularly concerning because it requires no special privileges or user interaction beyond the legitimate use of the patching functionality. Systems using bsdiff4 for software updates, firmware patches, or binary diff operations become vulnerable to this attack, making it a critical concern for software distribution platforms and update mechanisms.
The mitigation strategy for CVE-2020-15904 involves immediate upgrading to bsdiff4 version 1.2.0 or later, which contains the necessary fixes for the buffer overflow condition. Organizations should also implement additional defensive measures including patch file validation, sandboxed execution environments for patch processing, and monitoring for anomalous memory access patterns. The vulnerability aligns with several ATT&CK tactics including TA0002 Execution and TA0005 Defense Evasion, as it can be leveraged for code injection and system compromise. Security teams should conduct comprehensive vulnerability assessments to identify all systems using affected versions of bsdiff4 and establish monitoring procedures to detect potential exploitation attempts. The fix typically involves implementing proper bounds checking, input validation, and robust memory allocation practices that prevent the overflow condition from occurring during patch file processing operations.