unshar (unshar.c) in sharutils 4.2.1 allows local users to overwrite arbitrary files via a symlink attack on the unsh.X temporary file.

An updated sharutils package is now available.

This update has been rated as having low security impact by the Red Hat Security Response Team.

The sharutils package contains a set of tools for encoding and decoding packages of files in binary or text format.

A stack based overflow bug was found in the way shar handles the -o option. If a user can be tricked into running a specially crafted command, it could lead to arbitrary code execution. The Common Vulnerabilities and Exposures project (cve.mitre.org) has assigned the name CVE-2004-1772 to this issue. Please note that this issue does not affect Red Hat Enterprise Linux 4.

Two buffer overflow bugs were found in sharutils. If an attacker can place a malicious 'wc' command on a victim's machine, or trick a victim into running a specially crafted command, it could lead to arbitrary code execution. The Common Vulnerabilities and Exposures project (cve.mitre.org) has assigned the name CVE-2004-1773 to this issue.

A bug was found in the way unshar creates temporary files. A local user could use symlinks to overwrite arbitrary files the victim running unshar has write access to. The Common Vulnerabilities and Exposures project (cve.mitre.org) has assigned the name CVE-2005-0990 to this issue.

All users of sharutils should upgrade to this updated package, which includes backported fixes to correct these issues.

An Ubuntu Advisory reports :

Joey Hess discovered that 'unshar' created temporary files in an insecure manner. This could allow a symbolic link attack to create or overwrite arbitrary files with the privileges of the user invoking the program.

The remote Redhat Enterprise Linux 4 host has a package installed that is affected by multiple vulnerabilities as referenced in the RHSA-2005:377 advisory.

    The sharutils package contains a set of tools for encoding and decoding     packages of files in binary or text format.

    A stack based overflow bug was found in the way shar handles the -o option.
    If a user can be tricked into running a specially crafted command, it could     lead to arbitrary code execution.  The Common Vulnerabilities and Exposures     project (cve.mitre.org) has assigned the name CAN-2004-1772 to this issue.
    Please note that this issue does not affect Red Hat Enterprise Linux 4.

    Two buffer overflow bugs were found in sharutils. If an attacker can place     a malicious 'wc' command on a victim's machine, or trick a victim into     running a specially crafted command, it could lead to arbitrary code     execution.  The Common Vulnerabilities and Exposures project     (cve.mitre.org) has assigned the name CAN-2004-1773 to this issue.

    A bug was found in the way unshar creates temporary files. A local user     could use symlinks to overwrite arbitrary files the victim running unshar     has write access to. The Common Vulnerabilities and Exposures project     (cve.mitre.org) has assigned the name CAN-2005-0990 to this issue.

    All users of sharutils should upgrade to this updated package, which     includes backported fixes to correct these issues.

Tenable has extracted the preceding description block directly from the Red Hat Enterprise Linux security advisory.

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

Shaun Colley discovered a buffer overflow in shar that was triggered by output files (using -o) with names longer than 49 characters which could be exploited to run arbitrary attacker-specified code.

Ulf Harnhammar discovered that shar does not check the data length returned by the wc command.

Joey Hess discovered that unshar would create temporary files in an insecure manner which could allow a symbolic link attack to create or overwrite arbitrary files with the privileges of the user using unshar.

The updated packages have been patched to correct these issues.

ID	Name	Product	Family	Severity
21814	CentOS 3 / 4 : sharutils (CESA-2005:377)	Nessus	CentOS Local Security Checks	high
18952	FreeBSD : sharutils -- unshar insecure temporary file creation (5f003a08-ba3c-11d9-837d-000e0c2e438a)	Nessus	FreeBSD Local Security Checks	low
18147	RHEL 4 : sharutils (RHSA-2005:377)	Nessus	Red Hat Local Security Checks	high
18002	Mandrake Linux Security Advisory : sharutils (MDKSA-2005:067)	Nessus	Mandriva Local Security Checks	high

Detections

Analytics

CVE-2005-0990

critical

Tenable Plugins

high

low

high

high