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CVE-2020-29562: Glibc Denial of service

Virsec Security Research Lab Vulnerability Analysis

The Virsec Security Research Lab provides timely, relevant analysis about recent and notable security vulnerabilities.

1.1        Vulnerability Summary

The iconv function in the GNU C Library (aka glibc or libc6) 2.30 to 2.32, when converting UCS4 text containing an irreversible character, fails an assertion in the code path and aborts the program, potentially resulting in a denial of service. More Technical details are as below.

Picture6-1

Previously, in UCS4 conversion routines we limit the number of characters we examine to the minimum of the number of characters in the input and the number of characters in the output. This is not the correct behavior when __GCONV_IGNORE_ERRORS is set, as we do not consume an output character when we skip a code unit. Instead, track the input and output pointers and terminate the loop when either pointer reaches its limit.

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1.2        CVSS Score

The CVSS Base score of this vulnerability is 7.5 High.  CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

1.3        Affected Version

GNU C Library (aka glibc or libc6) 2.30 to 2.32.

1.4        Vulnerability Attribution

This vulnerability is reported by Michael Colavita.

1.5        Risk Impact

The GNU C Library project provides the core libraries for the GNU system and GNU/Linux systems, as well as many other systems that use Linux as the kernel. These libraries provide critical APIs including ISO C11, POSIX.1-2008, BSD, OS-specific APIs and more. These APIs include such foundational facilities as open, read, write, malloc, printf, getaddrinfo, dlopen, pthread_create, crypt, login, exit and more. The GNU C Library is designed to be a backwards compatible, portable, and high-performance ISO C library. It aims to follow all relevant standards including ISO C11, POSIX.1-2008, and IEEE 754-2008. Public exploit is not available, but looking at the code, it is possible to build one.

1.6        Virsec Security Platform (VSP) Support:

The Virsec Security Platform (VSP)- Memory monitors stack-based buffer overflows and will prevent any attempt by attacker to exploit this type of vulnerability.

VSP-Host monitors processes that are spawned which are not part of a set of whitelisted process. Any attempt to execute new command or unknown binary would be denied by VSP-Host’s Process Monitoring capability.

 

1.7        Reference Links:



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