[MediaWiki-l] [Wikitech-l] SHA-1 hash officially broken

Brion Vibber bvibber at wikimedia.org
Fri Feb 24 21:45:24 UTC 2017


Yes, keep an eye out for announcements about other software that might be
more seriously affected.

For instance Subversion source control has some problems which can cause
checksum errors when operating on a source tree that has had the malicious
pairs of files committed into to it:
https://arstechnica.com/security/2017/02/watershed-sha1-collision-just-broke-the-webkit-repository-others-may-follow/

My initial look at potential attacks on MediaWiki is that our case is less
severe; if conflicting files are uploaded they may trigger false
equivalency warnings (with each other only), and can overwrite each other
(but not other files) when deleted/undeleted. No errors would be thrown or
general data corruption would occur.

-- brion

On Fri, Feb 24, 2017 at 1:27 PM, Pine W <wiki.pine at gmail.com> wrote:

> As someone who runs a non-WMF MediaWiki installation and might set up at
> least one more, it's something that I want to know about. :) More info at
> https://phabricator.wikimedia.org/T158986, although if I understand the
> conversation on the Phabricator task correctly, the consensus is that
> migration off of SHA-1 for MediaWiki software is important but doesn't need
> to happen overnight because the attack is difficult to execute; however,
> possible attacks on other software that still runs SHA-1 should be
> considered. Is that correct, Brian?
>
> Pine
>
>
> On Fri, Feb 24, 2017 at 1:01 PM, Brian Wolff <bawolff at gmail.com> wrote:
>
> > Before anyone panics, this is not something that people who run mediawiki
> > wikis have to worry about.
> >
> > --
> > Brian
> >
> > On Friday, February 24, 2017, Pine W <wiki.pine at gmail.com> wrote:
> > > Forwarding info that may be of interest.
> > >
> > > Pine
> > >
> > >
> > > ---------- Forwarded message ----------
> > > From: Brion Vibber <bvibber at wikimedia.org>
> > > Date: Fri, Feb 24, 2017 at 9:56 AM
> > > Subject: [Wikitech-l] SHA-1 hash officially broken
> > > To: Wikimedia-tech list <wikitech-l at lists.wikimedia.org>
> > >
> > >
> > > Google security have announced that they have a working collision
> attack
> > > against the SHA-1 hash:
> > >
> > >
> > https://security.googleblog.com/2017/02/announcing-first-
> > sha1-collision.html
> > >
> > > It's highly recommended to move to sha-256 where doable.
> > >
> > > Note that MediaWiki uses sha-1 in a number of places; in some such as
> > > revision hashes it's advisory for tools only, but in other places like
> > > deleted files (filearchive table) we use it for addressing, and should
> > > consider steps to mitigate attacks swapping in alternate files during
> > > deletion/undeletion.
> > >
> > > -- brion
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