CVE-2021-41253
November 08, 2021
Zydis is an x86/x86-64 disassembler library. Users of Zydis versions v3.2.0 and older that use the string functions provided in `zycore` in order to append untrusted user data to the formatter buffer within their custom formatter hooks can run into heap buffer overflows. Older versions of Zydis failed to properly initialize the string object within the formatter buffer, forgetting to initialize a few fields, leaving their value to chance. This could then in turn cause zycore functions like `ZyanStringAppend` to make incorrect calculations for the new target size, resulting in heap memory corruption. This does not affect the regular uncustomized Zydis formatter, because Zydis internally doesn't use the string functions in zycore that act upon these fields. However, because the zycore string functions are the intended way to work with the formatter buffer for users of the library that wish to extend the formatter, we still consider this to be a vulnerability in Zydis. This bug is patched starting in version 3.2.1. As a workaround, users may refrain from using zycore string functions in their formatter hooks until updating to a patched version.
Related Resources (5)
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Contact UsCVSS v4
Base Score:
8.2
Attack Vector
NETWORK
Attack Complexity
HIGH
Attack Requirements
NONE
Privileges Required
NONE
User Interaction
NONE
Vulnerable System Confidentiality
NONE
Vulnerable System Integrity
NONE
Vulnerable System Availability
HIGH
Subsequent System Confidentiality
NONE
Subsequent System Integrity
NONE
Subsequent System Availability
NONE
CVSS v3
Base Score:
5.9
Attack Vector
NETWORK
Attack Complexity
HIGH
Privileges Required
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality
NONE
Integrity
NONE
Availability
HIGH
CVSS v2
Base Score:
6.8
Access Vector
NETWORK
Access Complexity
MEDIUM
Authentication
NONE
Confidentiality Impact
PARTIAL
Integrity Impact
PARTIAL
Availability Impact
PARTIAL
Weakness Type (CWE)
EPSS
Base Score:
0.55