CVE-2019-19637 in libsixel
Summary
by MITRE
An issue was discovered in libsixel 1.8.2. There is an integer overflow in the function sixel_decode_raw_impl at fromsixel.c.
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Analysis
by VulDB Data Team • 03/09/2024
The vulnerability identified as CVE-2019-19637 represents a critical integer overflow flaw within the libsixel library version 1.8.2, specifically within the sixel_decode_raw_impl function located in the fromsixel.c source file. This library serves as a decoder for sixel graphics format, commonly used for displaying bitmap images in terminal environments and legacy systems. The integer overflow occurs when processing malformed sixel data streams, creating a condition where arithmetic operations exceed the maximum representable value for the integer data type, potentially leading to unpredictable behavior and system instability.
The technical exploitation of this vulnerability stems from the improper handling of integer values during the decoding process of sixel graphics data. When the sixel_decode_raw_impl function processes input data, it fails to adequately validate or constrain integer calculations that determine buffer sizes or loop iterations. This oversight allows an attacker to craft malicious sixel data sequences that trigger the overflow condition, potentially causing the application to allocate insufficient memory or execute operations with incorrect parameters. The vulnerability manifests as an integer overflow in the context of the sixel format decoder, which operates under the assumption that input parameters will remain within expected bounds, but fails to account for maliciously constructed inputs that deliberately exceed these boundaries.
The operational impact of this vulnerability extends beyond simple application crashes or hangs, as it creates potential vectors for more severe security consequences. Systems utilizing libsixel for image processing in terminal environments, such as legacy mainframe terminals, certain text-based interfaces, or specialized applications handling sixel graphics, become susceptible to denial of service attacks or potentially arbitrary code execution. The vulnerability affects any software that depends on libsixel 1.8.2 for sixel graphics decoding, including terminal emulators, text-based image viewers, and specialized communication applications. Attackers could exploit this flaw by providing specially crafted sixel data to applications using the vulnerable library, potentially leading to system instability, resource exhaustion, or in worst-case scenarios, remote code execution depending on the application's memory management practices.
Mitigation strategies for CVE-2019-19637 should prioritize immediate library updates to versions that address the integer overflow issue, as this represents the most effective defense against exploitation. System administrators should conduct thorough inventory assessments to identify all applications and systems utilizing libsixel 1.8.2, particularly those in critical infrastructure or sensitive environments. Input validation measures should be implemented at the application level to sanitize sixel data before processing, including bounds checking and parameter validation to prevent malformed data from reaching the vulnerable library functions. Additionally, deployment of network segmentation and access controls can limit the potential impact of exploitation attempts, while regular security monitoring and vulnerability scanning should be maintained to detect any unauthorized attempts to exploit this flaw. This vulnerability aligns with CWE-190, Integer Overflow or Wraparound, and may map to ATT&CK techniques involving privilege escalation through software vulnerabilities. Organizations should also consider implementing runtime protections and application whitelisting to prevent execution of untrusted sixel data streams, while maintaining comprehensive incident response procedures for potential exploitation attempts.