CVE-2017-8871 in libcroco
Summary
by MITRE
The cr_parser_parse_selector_core function in cr-parser.c in libcroco 0.6.12 allows remote attackers to cause a denial of service (infinite loop and CPU consumption) via a crafted CSS file.
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Analysis
by VulDB Data Team • 12/08/2024
The vulnerability identified as CVE-2017-8871 resides within the libcroco library version 0.6.12, specifically within the cr_parser_parse_selector_core function located in the cr-parser.c file. This flaw represents a classic denial of service vulnerability that can be exploited by remote attackers through the careful crafting of malicious CSS files. The library serves as a CSS parsing component widely used in various applications and web browsers for processing Cascading Style Sheets, making this vulnerability particularly concerning due to its potential for widespread impact. The issue manifests as an infinite loop during the parsing process, leading to excessive CPU consumption that can effectively render systems unresponsive or cause complete service disruption.
The technical nature of this vulnerability stems from inadequate input validation and loop termination conditions within the CSS selector parsing logic. When the cr_parser_parse_selector_core function encounters a specially crafted CSS file, it fails to properly handle certain malformed or recursive selector patterns that cause the parser to enter an infinite loop. This flaw falls under the category of CWE-835, which specifically addresses the issue of loops with insufficient exit conditions, making it a clear example of improper loop control logic. The parser's inability to gracefully handle malformed input demonstrates a fundamental flaw in the defensive programming practices employed within the library's codebase.
The operational impact of this vulnerability extends beyond simple service disruption, as it can be leveraged by attackers to perform resource exhaustion attacks against systems that rely on libcroco for CSS processing. Applications that process user-uploaded CSS content, web browsers that utilize the library, or any system that parses external CSS files become potential targets for this attack vector. The infinite loop consumes CPU resources continuously, potentially leading to system instability, application crashes, or complete system unavailability. This type of vulnerability aligns with ATT&CK technique T1499.004, which covers resource exhaustion attacks, and demonstrates how seemingly benign parsing operations can become weaponized for denial of service purposes.
Mitigation strategies for CVE-2017-8871 should focus on immediate library updates to versions that have addressed this parsing flaw. System administrators and developers should prioritize patching affected installations, as the vulnerability has been resolved in subsequent releases of libcroco. Additionally, implementing input validation measures that limit the complexity and size of CSS files processed by applications can provide defense-in-depth. The use of sandboxed parsing environments or timeout mechanisms for CSS processing operations can also help prevent exploitation. Organizations should also consider implementing monitoring for unusual CPU consumption patterns that might indicate exploitation attempts. The vulnerability serves as a reminder of the critical importance of robust input validation and proper loop termination in security-sensitive code, particularly in libraries that process untrusted data from external sources.