CVE-2021-20294 in Binutils
Summary
by MITRE • 04/29/2021
A flaw was found in binutils readelf 2.35 program. An attacker who is able to convince a victim using readelf to read a crafted file could trigger a stack buffer overflow, out-of-bounds write of arbitrary data supplied by the attacker. The highest impact of this flaw is to confidentiality, integrity, and availability.
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Analysis
by VulDB Data Team • 05/03/2021
The vulnerability identified as CVE-2021-20294 resides within the binutils readelf utility version 2.35, representing a critical stack buffer overflow flaw that can be exploited through crafted input files. This issue affects the core functionality of readelf, which is designed to display information about binary files and their sections, making it a fundamental tool in software development, debugging, and security analysis. The flaw stems from inadequate bounds checking during the parsing of ELF (Executable and Linkable Format) files, specifically when processing certain header structures and section data that exceed allocated buffer sizes on the stack.
The technical implementation of this vulnerability involves a classic stack-based buffer overflow condition where attacker-controlled data is processed without proper validation of input boundaries. When readelf encounters a specially crafted ELF file containing oversized or malformed section headers, the program fails to validate the size parameters before copying data into fixed-size stack buffers. This allows an attacker to overwrite adjacent stack memory locations with arbitrary data, potentially leading to arbitrary code execution or system compromise. The vulnerability is particularly concerning because readelf is commonly used in automated build systems, security analysis tools, and development environments where users may unknowingly process untrusted binary files from external sources.
The operational impact of this vulnerability extends across multiple security domains including confidentiality, integrity, and availability as indicated in the CVE description. An attacker could leverage this flaw to execute arbitrary code with the privileges of the user running readelf, potentially leading to complete system compromise. The confidentiality aspect is compromised through potential data leakage via memory corruption that could expose sensitive information stored in adjacent stack memory locations. Integrity is at risk due to the possibility of arbitrary memory modification that could corrupt program state or inject malicious code into running processes. Availability is threatened through potential denial-of-service conditions where the buffer overflow could cause application crashes or system instability during normal operation.
This vulnerability maps directly to CWE-121 Stack-based Buffer Overflow and CWE-787 Out-of-bounds Write, both of which are classified as high-severity issues in the Common Weakness Enumeration catalog. The attack pattern aligns with ATT&CK technique T1059.007 Command and Scripting Interpreter: Unix Shell, where adversaries may use command-line tools to execute malicious code through crafted file inputs. The exploitability of this vulnerability is enhanced by the widespread use of readelf in various automation contexts, including continuous integration pipelines, security scanning tools, and system administration scripts where untrusted input processing is common. Organizations should implement immediate mitigations including updating to patched versions of binutils, implementing input validation measures, and restricting execution privileges for readelf in automated environments to prevent potential exploitation.
The remediation approach requires comprehensive system updates to binutils version 2.36 or later, which contain the necessary patches addressing the buffer overflow conditions. Security teams should conduct thorough inventory assessments to identify all systems running vulnerable versions of readelf and prioritize patching based on risk exposure. Additional defensive measures include implementing sandboxing techniques for processing untrusted binary files, deploying input validation controls, and establishing secure coding practices for applications that may invoke readelf or similar tools. Network security controls should monitor for suspicious file processing activities and implement principle of least privilege access controls to limit the impact of potential exploitation. Organizations should also consider implementing automated vulnerability scanning tools that can detect and alert on the presence of vulnerable readelf installations in their environments.