NULL dereference when decompressing specially crafted archives

[Daniel Axtens]

Hi,

Fuzzing tar with checksums disabled reveals a NULL pointer dereference when parsing certain archives that have malformed extended headers. This affects tar from (at least) Trusty, Bionic and Cosmic. I haven't tested Xenial's version.

A test case with fixed checksums is attached. To avoid breaking anything that looks inside tar archives, I have converted it to text with xxd. To reproduce:

$ xxd -r gnutar-crash.tar.txt gnutar-crash.tar
$ tar Oxf gnutar-crash.tar
tar: Ignoring unknown extended header keyword 'GNU.sparse.minTr'
tar: Malformed extended header: missing length
Segmentation fault (core dumped)

I have also attached a patch against the latest upstream git and against 1.30 (in Cosmic). This fixes the issue by detecting the null result before it is dereferenced.

Regards,
Daniel

[Seth Arnold (seth-arnold)]

Hello Daniel, very nice.

Have you reported this issue upstream yet?

Thanks

[Daniel Axtens (daxtens)]

Hi Seth,

I've just learned how to navigate Savannah and reported it. I will let you know if/when they reply.

Regards,
Daniel

[Daniel Axtens (daxtens)]

This has been fixed in git: http://git.savannah.gnu.org/cgit/tar.git/commit/?id=cb07844454d8cc9fb21f53ace75975f91185a120

[Marc Deslauriers (mdeslaur)]

Can I make this bug public?

[Daniel Axtens (daxtens)]

The tar maintainers have disclosed the issue via the commit, so that sounds fine to me.

[Ubuntu Foundations Team Bug Bot (crichton)]

The attachment "patch against git head" seems to be a patch. If it isn't, please remove the "patch" flag from the attachment, remove the "patch" tag, and if you are a member of the ~ubuntu-reviewers, unsubscribe the team.

[This is an automated message performed by a Launchpad user owned by ~brian-murray, for any issues please contact him.]

[Seth Arnold (seth-arnold)]

Use CVE-2019-9923.

Thanks

[Jeffrey Hawkins (rtswguru)]

This issue is shown as Open on Jammy. The CVE is applicable to 1.32 and prior versions of TAR. Jammy uses 1.34, so this status should be not affected or closed. This was fixed in Focal in 1.30+dfsg-7ubuntu0.20.04.1. Please update the CVE status on Jammy.

[Jeffrey Hawkins (rtswguru)]

Update to my comment, issue is applicable to versions prior to 1.32 of TAR. Be that as it may, Jammy is not affected.

[Alex Murray (alexmurray)]

Thanks I have updated the status of this CVE in the Ubuntu CVE tracker.