A musl security update has been released for Debian GNU/Linux 9 LTS to address multiple bugs in handling of destination buffer size.

DLA 2474-1: musl security update

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Debian LTS Advisory DLA-2474-1 debian-lts@lists.debian.org
  https://www.debian.org/lts/security/ Utkarsh Gupta
December 01, 2020   https://wiki.debian.org/LTS
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Package : musl
Version : 1.1.16-3+deb9u1
CVE ID : CVE-2020-28928
Debian Bug : 975365

The wcsnrtombs function in all musl libc versions up through 1.2.1
has been found to have multiple bugs in handling of destination
buffer size when limiting the input character count, which can
lead to infinite loop with no forward progress (no overflow) or
writing past the end of the destination buffers.

For Debian 9 stretch, this problem has been fixed in version
1.1.16-3+deb9u1.

We recommend that you upgrade your musl packages.

For the detailed security status of musl please refer to
its security tracker page at:
  https://security-tracker.debian.org/tracker/musl

Further information about Debian LTS security advisories, how to apply
these updates to your system and frequently asked questions can be
found at:   https://wiki.debian.org/LTS