A nettle security update has been released for Debian GNU/Linux 9 LTS to address multiple vulnerabilities.

DLA 2760-1: nettle security update

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Debian LTS Advisory DLA-2760-1 debian-lts@lists.debian.org
  https://www.debian.org/lts/security/ Markus Koschany
September 18, 2021   https://wiki.debian.org/LTS
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Package : nettle
Version : 3.3-1+deb9u1
CVE ID : CVE-2021-3580 CVE-2021-20305
Debian Bug : 985652 989631

Multiple vulnerabilities were discovered in nettle, a low level
cryptographic library, which could result in denial of service (remote
crash in RSA decryption via specially crafted ciphertext, crash on ECDSA
signature verification) or incorrect verification of ECDSA signatures.

For Debian 9 stretch, these problems have been fixed in version
3.3-1+deb9u1.

We recommend that you upgrade your nettle packages.

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

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