CVE-2019-13050

Impact:
Moderate
Public Date:
2019-06-29
CWE:
CWE-297
Bugzilla:
1726146: CVE-2019-13050 GnuPG: interaction between the sks-keyserver code and GnuPG allows for a Certificate Spamming Attack which leads to persistent DoS

The MITRE CVE dictionary describes this issue as:

Interaction between the sks-keyserver code through 1.2.0 of the SKS keyserver network, and GnuPG through 2.2.16, makes it risky to have a GnuPG keyserver configuration line referring to a host on the SKS keyserver network. Retrieving data from this network may cause a persistent denial of service, because of a Certificate Spamming Attack.

Find out more about CVE-2019-13050 from the MITRE CVE dictionary dictionary and NIST NVD.

Statement

This is a certificate spamming attack, against key servers which use the sks-keyserver software. Attackers were able to poison some certificates in the SKS keyserver network. When GnuPG users import these certificate their installations will break. Currently there is no patch available for GnuPG. Users are encouraged to apply the mitigation mentioned on this page. Lastly there is no way to currently detect which certificates have been poisoned.

Users of GnuPG who import only locally created certificates or those created within their infrastructure and later use them for verification etc are not affected by this flaw.

CVSS v3 metrics

NOTE: The following CVSS v3 metrics and score provided are preliminary and subject to review.

CVSS3 Base Score 6.5
CVSS3 Base Metrics CVSS:3.0/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H
Attack Vector Network
Attack Complexity Low
Privileges Required None
User Interaction Required
Scope Unchanged
Confidentiality None
Integrity Impact None
Availability Impact High

Affected Packages State

Platform Package State
Red Hat Enterprise Linux 8 gnupg2 Affected
Red Hat Enterprise Linux 7 gnupg2 Affected
Red Hat Enterprise Linux 6 gnupg2 Affected
Red Hat Enterprise Linux 5 gnupg Out of support scope
Red Hat Enterprise Linux 5 gnupg2 Out of support scope
Unless explicitly stated as not affected, all previous versions of packages in any minor update stream of a product listed here should be assumed vulnerable, although may not have been subject to full analysis.

Mitigation

As per upstream: High-risk users should stop using the keyserver network immediately.

1. Open ~/.gnupg/gpg.conf in a text editor. Ensure there is no line starting with keyserver. If there is, remove it.
2. Open ~/.gnupg/dirmngr.conf in a text editor. Add the line "keyserver hkps://keys.openpgp.org" to the end of it.

keys.openpgp.org is a new experimental keyserver which is not part of the keyserver network and has some features which make it resistant to this attack. It is not a drop-in replacement: it has some limitations (for instance, its search functionality is sharply constrained). However, once you make this change you will be able to run gpg --refresh-keys with confidence.

For installations which are currently rendered unusable by this attack, the following repair method is advised:
1. If you know which certificate is likely poisoned, try deleting it. Once the installation becomes usable again, you can acquire a new unpoisoned copy of the certificate and re-import it.
2. If you do not know which certificate is poisoned, best option is to get a list of all your certificate IDs, delete your keyrings completely, and rebuild from scratch using known-good copies of the public certificates.

External References

Last Modified

CVE description copyright © 2017, The MITRE Corporation