4.3 - MDVSA-2010:246

Multiple vulnerabilities were discovered and corrected in krb5:

An unauthenticated remote attacker could alter a SAM-2 challenge, affecting the prompt text seen by the user or the kind of response sent to the KDC. Under some circumstances, this can negate the incremental security benefit of using a single-use authentication mechanism token. An unauthenticated remote attacker has a 1/256 chance of forging KRB-SAFE messages in an application protocol if the targeted pre-existing session uses an RC4 session key. Few application protocols use KRB-SAFE messages (CVE-2010-1323).

An unauthenticated remote attacker can forge GSS tokens that are intended to be integrity-protected but unencrypted, if the targeted pre-existing application session uses a DES session key. An authenticated remote attacker can forge PACs if using a KDC that does not filter client-provided PAC data. This can result in privilege escalation against a service that relies on PAC contents to make authorization decisions. An unauthenticated remote attacker has a 1/256 chance of swapping a client-issued KrbFastReq into a different KDC-REQ, if the armor key is RC4. The consequences are believed to be minor (CVE-2010-1324).

An authenticated remote attacker that controls a legitimate service principal has a 1/256 chance of forging the AD-SIGNEDPATH signature if the TGT key is RC4, allowing it to use self-generated evidence tickets for S4U2Proxy, instead of tickets obtained from the user or with S4U2Self. Configurations using RC4 for the TGT key are believed to be rare. An authenticated remote attacker has a 1/256 chance of forging AD-KDC-ISSUED signatures on authdata elements in tickets having an RC4 service key, resulting in privilege escalation against a service that relies on these signatures. There are no known uses of the KDC-ISSUED authdata container at this time (CVE-2010-4020.

An authenticated remote attacker that controls a legitimate service principal could obtain a valid service ticket to itself containing valid KDC-generated authorization data for a client whose TGS-REQ it has intercepted. The attacker could then use this ticket for S4U2Proxy to impersonate the targeted client even if the client never authenticated to the subverted service. The vulnerable configuration is believed to be rare (CVE-2010-4021).

The updated packages have been patched to correct this issue.