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

DLA 2504-1: mediawiki security update

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Debian LTS Advisory DLA-2504-1 debian-lts@lists.debian.org
  https://www.debian.org/lts/security/ Roberto C. Sánchez
December 22, 2020   https://wiki.debian.org/LTS
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Package : mediawiki
Version : 1:1.27.7-1~deb9u7
CVE ID : CVE-2020-15005 CVE-2020-35477 CVE-2020-35479 CVE-2020-35480

Multiple security issues were discovered in MediaWiki, a website engine
for collaborative work.

CVE-2020-15005

Private wikis behind a caching server using the img_auth.php image
authorization security feature may have had their files cached
publicly, so any unauthorized user could view them.

CVE-2020-35477

Blocks legitimate attempts to hide log entries in some situations.

CVE-2020-35479

Allows XSS via BlockLogFormatter.php. Language::translateBlockExpiry
itself does not escape in all code paths. For example, the return of
Language::userTimeAndDate is is always unsafe for HTML in a month
value.

CVE-2020-35480

Missing users (accounts that don't exist) and hidden users (accounts
that have been explicitly hidden due to being abusive, or similar)
that the viewer cannot see are handled differently, exposing
sensitive information about the hidden status to unprivileged
viewers.

For Debian 9 stretch, these problems have been fixed in version
1:1.27.7-1~deb9u7.

We recommend that you upgrade your mediawiki packages.

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

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