Tavis Ormandy discovered a potential weakness in the signature verification of gnupg. gpgv and gpg --verify returned a successful exit code even if the checked file did not have any signature at all.
The recommended way of checking the result is to evaluate the status messages, but some third-party applications might just check the exit code for determining whether or not a signature is valid. These applications could be tricked into erroneously reporting a valid signature.

Please note that this does not affect the Ubuntu package signature checks.

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

The remote Redhat Enterprise Linux 4 host has a package installed that is affected by multiple vulnerabilities as referenced in the RHSA-2006:0266 advisory.

  - security flaw (CVE-2006-0049, CVE-2006-0455)

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

The remote host is affected by the vulnerability described in GLSA-200602-10 (GnuPG: Incorrect signature verification)

    Tavis Ormandy of the Gentoo Linux Security Auditing Team     discovered that automated systems relying on the return code of GnuPG     or gpgv to authenticate digital signatures may be misled by malformed     signatures. GnuPG documentation states that a return code of zero (0)     indicates success, however gpg and gpgv may also return zero if no     signature data was found in a detached signature file.
  Impact :

    An attacker may be able to bypass authentication in automated     systems relying on the return code of gpg or gpgv to authenticate     digital signatures.
  Workaround :

    There is no known workaround at this time.

Werner Koch reports :

The Gentoo project identified a security related bug in GnuPG. When using any current version of GnuPG for unattended signature verification (e.g. by scripts and mail programs), false positive signature verification of detached signatures may occur.

This problem affects the tool *gpgv*, as well as using 'gpg --verify' to imitate gpgv, if only the exit code of the process is used to decide whether a detached signature is valid. This is a plausible mode of operation for gpgv.

If, as suggested, the --status-fd generated output is used to decide whether a signature is valid, no problem exists. In particular applications making use of the GPGME library[2] are not affected.

Tavis Ormandy noticed that gnupg, the GNU privacy guard - a free PGP replacement, verifies external signatures of files successfully even though they don't contain a signature at all.

Tavis Ormandy discovered it is possible to make gpg incorrectly return success when verifying an invalid signature file.

The updated packages have been patched to address this issue.

The GNU Privacy Guard provides encryption and signing for messages and arbitrary files, and implements the OpenPGP standard as described by IETF RFC2440.

Version 1.4.2 of GnuPG would in some cases erroneously exit with status 0 (signaling no errors) if it was invoked to check a signature but found no signature to check. This should be corrected in version 1.4.2.1.

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

New GnuPG packages are available for Slackware 9.0, 9.1, 10.0, 10.1, 10.2, and -current to fix security issues.

An updated GnuPG package that fixes signature verification flaws as well as minor bugs is now available.

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

GnuPG is a utility for encrypting data and creating digital signatures.

Tavis Ormandy discovered a bug in the way GnuPG verifies cryptographically signed data with detached signatures. It is possible for an attacker to construct a cryptographically signed message which could appear to come from a third party. When a victim processes a GnuPG message with a malformed detached signature, GnuPG ignores the malformed signature, processes and outputs the signed data, and exits with status 0, just as it would if the signature had been valid. In this case, GnuPG's exit status would not indicate that no signature verification had taken place. This issue would primarily be of concern when processing GnuPG results via an automated script. The Common Vulnerabilities and Exposures project assigned the name CVE-2006-0455 to this issue.

Tavis Ormandy also discovered a bug in the way GnuPG verifies cryptographically signed data with inline signatures. It is possible for an attacker to inject unsigned data into a signed message in such a way that when a victim processes the message to recover the data, the unsigned data is output along with the signed data, gaining the appearance of having been signed. This issue is mitigated in the GnuPG shipped with Red Hat Enterprise Linux as the --ignore-crc-error option must be passed to the gpg executable for this attack to be successful.
The Common Vulnerabilities and Exposures project assigned the name CVE-2006-0049 to this issue.

Please note that neither of these issues affect the way RPM or up2date verify RPM package files, nor is RPM vulnerable to either of these issues.

All users of GnuPG are advised to upgrade to this updated package, which contains backported patches to correct these issues.

ID	Name	Product	Family	Published	Updated	Severity
21071	Ubuntu 4.10 / 5.04 / 5.10 : gnupg vulnerability (USN-252-1)	Nessus	Ubuntu Local Security Checks	3/13/2006	1/19/2021	medium
21090	RHEL 4 : gnupg (RHSA-2006:0266)	Nessus	Red Hat Local Security Checks	3/16/2006	4/24/2024	high
20938	GLSA-200602-10 : GnuPG: Incorrect signature verification	Nessus	Gentoo Local Security Checks	2/19/2006	1/6/2021	medium
21442	FreeBSD : gnupg -- false positive signature verification (63fe4189-9f97-11da-ac32-0001020eed82)	Nessus	FreeBSD Local Security Checks	5/13/2006	1/6/2021	medium
22844	Debian DSA-978-1 : gnupg - programming error	Nessus	Debian Local Security Checks	10/14/2006	1/4/2021	medium
20942	Mandrake Linux Security Advisory : gnupg (MDKSA-2006:043)	Nessus	Mandriva Local Security Checks	2/19/2006	1/6/2021	medium
20937	Fedora Core 4 : gnupg-1.4.2.1-1 (2006-116)	Nessus	Fedora Local Security Checks	2/19/2006	1/11/2021	medium
21075	Slackware 10.0 / 10.1 / 10.2 / 9.0 / 9.1 / current : gnupg (SSA:2006-072-02)	Nessus	Slackware Local Security Checks	3/14/2006	1/14/2021	medium
21990	CentOS 3 / 4 : gnu / gnupg (CESA-2006:0266)	Nessus	CentOS Local Security Checks	7/5/2006	1/4/2021	medium

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