CVE-2020-6618 in stb
Summary
by MITRE
stb stb_truetype.h through 1.22 has a heap-based buffer over-read in stbtt__find_table.
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Analysis
by VulDB Data Team • 03/20/2024
The vulnerability identified as CVE-2020-6618 affects the stb_truetype.h library version 1.22 and earlier, representing a heap-based buffer over-read condition that occurs within the stbtt__find_table function. This issue arises from improper bounds checking during the processing of truetype font files, specifically when the library attempts to locate table headers within font data structures. The flaw is particularly concerning as it demonstrates a classic memory safety issue where the application reads data beyond the allocated buffer boundaries, potentially leading to information disclosure or system instability.
The technical implementation of this vulnerability stems from the stbtt__find_table function's failure to validate input parameters properly when parsing font table offsets. When processing malformed or specially crafted font files, the function does not adequately verify that table offsets fall within the bounds of the available font data buffer. This allows an attacker to manipulate the font parsing logic through carefully constructed input data, causing the library to read memory locations that extend beyond the intended buffer limits. The vulnerability is classified as a heap-based buffer over-read under CWE-125, which represents an insufficient boundary check that allows reading beyond allocated memory regions. This particular flaw demonstrates how font parsing libraries can become attack vectors when they fail to properly validate the structure and content of input files.
The operational impact of this vulnerability extends beyond simple memory corruption, as it can potentially be exploited in various attack scenarios including remote code execution when the vulnerable library is used in web browsers, font rendering systems, or document processing applications. When exploited, the over-read condition may expose sensitive memory contents such as stack canaries, heap metadata, or other application data that could be leveraged for further exploitation. The vulnerability affects any system that utilizes the stb_truetype.h library for font processing, including web browsers that support truetype fonts, desktop applications, and mobile platforms. According to ATT&CK framework, this vulnerability aligns with T1203 - Exploitation for Client Execution and T1068 - Exploitation for Privilege Escalation, as it represents a client-side exploitation vector that could potentially lead to privilege escalation when combined with other attack primitives.
Mitigation strategies for CVE-2020-6618 primarily focus on updating to the patched version of the stb_truetype.h library, which implements proper bounds checking in the stbtt__find_table function. System administrators should prioritize updating all applications and services that depend on this library, particularly those handling user-provided font data. Additionally, implementing input validation measures such as sanitizing font file inputs and employing memory protection mechanisms like address space layout randomization can help reduce the exploitability of this vulnerability. The fix typically involves adding proper bounds checking before accessing buffer locations and ensuring that all table offset calculations are validated against the actual size of the font data buffer. Organizations should also consider implementing network-level filtering to prevent the processing of untrusted font files and maintain regular vulnerability assessments to identify other potential instances of similar issues within their font processing pipelines.