CVE-2018-12911 in WebkitGTK+
Summary
by MITRE
WebKitGTK+ 2.20.3 has an off-by-one error, with a resultant out-of-bounds write, in the get_simple_globs functions in ThirdParty/xdgmime/src/xdgmimecache.c and ThirdParty/xdgmime/src/xdgmimeglob.c.
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Analysis
by VulDB Data Team • 04/18/2023
The vulnerability CVE-2018-12911 represents a critical memory corruption issue affecting WebKitGTK+ version 2.20.3, specifically within the xdgmime library components that handle MIME type handling for web content. This flaw manifests as an off-by-one error in the get_simple_globs functions located in two key files within the ThirdParty/xdgmime/src directory structure. The issue stems from improper boundary checking during string processing operations where the application fails to validate array indices against their allocated bounds, creating a scenario where memory access extends beyond intended limits. Such vulnerabilities are particularly dangerous in browser engine contexts as they can be exploited to execute arbitrary code or cause application crashes through memory corruption attacks.
The technical implementation of this vulnerability occurs when the get_simple_globs functions process MIME type patterns and glob expressions used for file association handling in web applications. The off-by-one error specifically affects how the functions calculate and validate string boundaries when parsing wildcard patterns and file extension mappings. When processing certain malformed or specially crafted MIME type definitions, the code fails to properly account for the terminating null byte or boundary conditions, resulting in one additional byte being written beyond the allocated memory buffer. This out-of-bounds write operation can overwrite adjacent memory locations, potentially corrupting critical data structures, function pointers, or control flow information within the application's memory space. The vulnerability aligns with CWE-129, which describes improper validation of array indices, and CWE-787, which covers out-of-bounds write conditions.
The operational impact of this vulnerability extends beyond simple application instability, presenting significant security risks when exploited in web browsing contexts. Attackers could leverage this flaw by crafting malicious web content or MIME type definitions that trigger the vulnerable code path during normal browser operation. The out-of-bounds write could potentially overwrite function return addresses, stack canaries, or other critical memory structures, enabling arbitrary code execution with the privileges of the affected browser process. This makes the vulnerability particularly attractive to threat actors seeking to compromise user systems through drive-by downloads or malicious websites. The issue affects WebKitGTK+ implementations that rely on the xdgmime library for proper MIME type handling, which is integral to web browser functionality for content rendering and file association management. According to ATT&CK framework category T1059, this vulnerability could be exploited through command and scripting interpreter techniques, while T1190 represents the use of exploitation for execution purposes.
Mitigation strategies for CVE-2018-12911 primarily focus on immediate software updates and patches provided by the WebKitGTK+ maintainers, as the vulnerability resides in third-party library components that require coordinated fixes. System administrators should prioritize updating to WebKitGTK+ versions that include patches addressing the specific off-by-one error in the xdgmime library functions. Additionally, implementing network-level protections such as web application firewalls and content filtering systems can help reduce exposure by blocking malicious MIME type patterns before they reach vulnerable applications. Memory protection mechanisms like stack canaries, address space layout randomization, and data execution prevention should also be enabled to mitigate potential exploitation attempts. Organizations should conduct thorough vulnerability assessments to identify all systems running affected WebKitGTK+ versions and implement remediation schedules that prioritize critical systems. The fix typically involves correcting the boundary validation logic in the get_simple_globs functions to ensure proper array indexing and memory allocation handling, preventing the out-of-bounds write condition that enables exploitation.