pam-krb5 before 4.9 has a buffer overflow that might cause remote code execution in situations involving supplemental prompting by a Kerberos library. It may overflow a buffer provided by the underlying Kerberos library by a single '\0' byte if an attacker responds to a prompt with an answer of a carefully chosen length. The effect may range from heap corruption to stack corruption depending on the structure of the underlying Kerberos library, with unknown effects but possibly including code execution. This code path is not used for normal authentication, but only when the Kerberos library does supplemental prompting, such as with PKINIT or when using the non-standard no_prompt PAM configuration option.

The remote Ubuntu 16.04 LTS / 18.04 LTS host has packages installed that are affected by a vulnerability as referenced in the USN-4314-1 advisory.

    Russ Allbery discovered that pam-krb5 incorrectly handled some responses. An attacker could possibly use     this issue to execute arbitrary code.

Tenable has extracted the preceding description block directly from the Ubuntu security advisory.

Note that Nessus has not tested for this issue but has instead relied only on the application's self-reported version number.

Russ Allbery discovered a buffer overflow in the PAM module for MIT Kerberos, which could result in denial of service or potentially the execution of arbitrary code.

The krb5 PAM module (pam_krb5.so) had a buffer overflow that might have caused remote code execution in situations involving supplemental prompting by a Kerberos library. It might have overflown a buffer provided by the underlying Kerberos library by a single '\0' byte if an attacker responded to a prompt with an answer of a carefully chosen length. The effect may have ranged from heap corruption to stack corruption depending on the structure of the underlying Kerberos library, with unknown effects but possibly including code execution.
This code path had not been used for normal authentication, but only when the Kerberos library did supplemental prompting, such as with PKINIT or when using the non-standard no_prompt PAM configuration option.

For Debian 8 'Jessie', this problem has been fixed in version 4.6-3+deb8u1. The fix was prepared by Mike Gabriel.

We recommend that you upgrade your libpam-krb5 packages.

NOTE: Tenable Network Security has extracted the preceding description block directly from the DLA security advisory. Tenable has attempted to automatically clean and format it as much as possible without introducing additional issues.

ID	Name	Product	Family	Severity
135170	Ubuntu 16.04 LTS / 18.04 LTS : pam-krb5 vulnerability (USN-4314-1)	Nessus	Ubuntu Local Security Checks	critical
135103	Debian DSA-4648-1 : libpam-krb5 - security update	Nessus	Debian Local Security Checks	critical
135101	Debian DLA-2166-1 : libpam-krb5 security update	Nessus	Debian Local Security Checks	critical

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CVE-2020-10595

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