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critical advisory

CVE-2020-37239 - libbabl Double Free Vulnerability

libbabl 0.1.62 contains a double free vulnerability, identified as CVE-2020-37239, that allows attackers to bypass memory safety checks by exploiting signature overwriting in freed chunks, potentially leading to memory corruption and code execution.

libbabl version 0.1.62 contains a critical vulnerability (CVE-2020-37239) related to double free detection. The vulnerability allows an attacker to bypass memory safety mechanisms by exploiting signature overwrites within freed memory chunks. Specifically, the issue arises when babl_free() is called twice on the same memory address. The standard C library’s (libc) malloc metadata overwrites libbabl’s signature field upon the initial free() call. This overwrite prevents the double-free detection mechanism from triggering on the subsequent babl_free() call, which could lead to memory corruption and arbitrary code execution. This vulnerability poses a significant risk to applications using the affected libbabl version.

Attack Chain

  1. An application using libbabl 0.1.62 allocates memory using babl_malloc().
  2. The allocated memory block contains babl’s metadata including a signature field.
  3. The application calls babl_free() on the allocated memory block.
  4. libc’s free() function overwrites babl’s metadata signature field with malloc metadata.
  5. The application erroneously calls babl_free() again on the same memory block.
  6. Due to the overwritten signature, babl’s double-free detection mechanism fails.
  7. The memory is freed again, corrupting the heap metadata.
  8. Subsequent memory allocations may lead to arbitrary code execution due to the corrupted heap.

Impact

Successful exploitation of CVE-2020-37239 can lead to memory corruption and potentially arbitrary code execution within the context of the application using libbabl 0.1.62. This could allow an attacker to gain control of the application, potentially leading to data breaches, system compromise, or denial of service. Given the low level of interaction required to trigger the vulnerability, the impact is potentially very high.

Recommendation

  • Upgrade to a patched version of libbabl that addresses CVE-2020-37239.
  • Apply memory debugging tools during development to identify and prevent double-free conditions in code that utilizes libbabl.
  • Monitor applications utilizing libbabl for unusual memory allocation patterns that may indicate exploitation attempts.

Detection coverage 2

Detect CVE-2020-37239 Exploitation Attempt - Double Free

high

Detects potential exploitation of CVE-2020-37239 by monitoring for double free attempts in libbabl applications based on process execution patterns.

sigma tactics: defense_evasion techniques: T1068 sources: process_creation, linux

Detect Suspicious Memory Allocation Patterns Related to libbabl

medium

Detects suspicious memory allocation patterns potentially indicative of double-free vulnerability exploitation attempts related to libbabl.

sigma tactics: defense_evasion techniques: T1068 sources: process_creation, linux

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