CVE-2020-29562: 
NixOS vulnerability analysis and mitigation

The GNU C Library (glibc) versions 2.30 to 2.32 contained a vulnerability identified as CVE-2020-29562. The vulnerability was discovered in the iconv function when converting UCS4 text containing an irreversible character, which could cause an assertion failure in the code path and abort the program (NVD, Sourceware Bug).

The vulnerability stems from improper bounds used when converting UCS4 to the internal UCS4-like format. The issue occurs specifically in the __gconv_transform_ucs4_internal function where an assertion outbuf == outerr fails. The vulnerability has been assigned a CVSS v3.1 base score of 4.8 (Medium) with the vector string CVSS:3.1/AV:N/AC:H/PR:L/UI:R/S:U/C:N/I:N/A:H (NVD, Sourceware Bug).

When successfully exploited, this vulnerability could result in a denial of service (DoS) condition by causing the program to abort due to the assertion failure. This affects applications that use the iconv function for character set conversion, particularly when handling UCS4 text with irreversible characters (NetApp Advisory).

The vulnerability requires specific conditions to be exploited, including the presence of UCS4 text containing an irreversible character. The issue was confirmed reproducible through a test case that triggers the assertion failure in the iconv function (Sourceware Bug).

The vulnerability was fixed in glibc by modifying the UCS4 conversion routines to correctly track input and output pointers and terminate the loop when either reaches its limit. The fix was committed to the master branch with commit 228edd356f03bf62dcf2b1335f25d43c602ee68d. Users are advised to upgrade to patched versions of glibc (Sourceware Bug, Gentoo Advisory).