An obfs4proxy security update has been released for Debian GNU/Linux 9 LTS to address an issue in supplementary Go cryptography libraries.

DLA 2442-1: obfs4proxy security update

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Debian LTS Advisory DLA-2442-1 debian-lts@lists.debian.org
  https://www.debian.org/lts/security/ Brian May
November 10, 2020   https://wiki.debian.org/LTS
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Package : obfs4proxy
Version : 0.0.7-1+deb8u1
CVE ID : CVE-2019-11840

golang-go.crypto was recently updated with a fix for CVE-2019-11840. This in
turn requires all packages that use the affected code to be recompiled in order
to pick up the security fix.

CVE-2019-11840

An issue was discovered in supplementary Go cryptography libraries, aka
golang-googlecode-go-crypto. If more than 256 GiB of keystream is
generated, or if the counter otherwise grows greater than 32 bits, the amd64
implementation will first generate incorrect output, and then cycle back to
previously generated keystream. Repeated keystream bytes can lead to loss of
confidentiality in encryption applications, or to predictability in CSPRNG
applications.

For Debian 9 stretch, this problem has been fixed in version3
0.0.7-1+deb8u1.

We recommend that you upgrade your obfs4proxy packages.

For the detailed security status of obfs4proxy please refer to
its security tracker page at:
  https://security-tracker.debian.org/tracker/obfs4proxy

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