CVE-2020-24822 in Libelfin
Summary
by MITRE • 08/04/2021
A vulnerability in the dwarf::cursor::uleb function of Libelfin v0.3 allows attackers to cause a denial of service (DOS) through a segmentation fault via a crafted ELF file.
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Analysis
by VulDB Data Team • 08/08/2021
The vulnerability identified as CVE-2020-24822 resides within the libelfin library version 0.3, specifically affecting the dwarf::cursor::uleb function implementation. This flaw represents a classic buffer over-read condition that manifests when processing malformed ELF files containing crafted dwarf debugging information. The issue stems from insufficient input validation and boundary checking within the unsigned leb128 decoding routine, which is fundamental to parsing dwarf debugging data structures. When an attacker supplies a specially constructed ELF file with malformed dwarf sections, the uleb function attempts to read beyond the allocated buffer boundaries, resulting in a segmentation fault and subsequent process termination.
This vulnerability operates at the intersection of software security and binary analysis, where the parsing of debugging information becomes a vector for system instability. The uleb128 encoding scheme, widely used in dwarf debugging formats, employs variable-length encoding for unsigned integers, with each byte containing seven bits of data and a continuation bit in the most significant bit. The flaw occurs when the parsing logic fails to properly validate the continuation bits or check buffer boundaries, allowing an attacker to craft a sequence that causes the cursor to advance beyond valid memory regions. The attack requires minimal privileges since the vulnerability is triggered during normal file processing operations, making it particularly dangerous in environments where arbitrary file processing occurs.
The operational impact of CVE-2020-24822 extends beyond simple denial of service, as it can be exploited in various contexts where libelfin is utilized for ELF file analysis. Systems that process user-uploaded files, perform binary analysis, or handle debugging information from untrusted sources become vulnerable to this attack vector. The vulnerability affects applications and tools that rely on libelfin for parsing dwarf debugging information, including but not limited to system diagnostic tools, binary analyzers, and development environments. The segmentation fault resulting from this flaw can cause cascading failures in applications that do not properly handle such exceptions, potentially leading to broader system instability or service disruption. From an attacker perspective, this represents a low-effort, high-impact method for causing system downtime or resource exhaustion, particularly in environments where automated processing of binary files is common.
Mitigation strategies for CVE-2020-24822 primarily involve upgrading to a patched version of libelfin where the uleb128 parsing logic has been corrected to include proper boundary checks and input validation. Security practitioners should implement defensive programming practices such as implementing input sanitization routines and establishing robust error handling mechanisms around dwarf parsing operations. The vulnerability aligns with CWE-129, which addresses improper validation of array indices, and demonstrates characteristics consistent with ATT&CK technique T1499.001, focusing on network denial of service through system resource exhaustion. Organizations should also consider implementing automated scanning for vulnerable libraries and establishing monitoring for unusual segmentation fault patterns in systems processing ELF files. Additionally, runtime protections such as address space layout randomization and stack canaries can provide defense-in-depth measures against exploitation attempts, though the primary remediation remains the software patch addressing the core parsing logic flaw.