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| Daniel Bleichenbacher recently described an attack on OpenSSL PKCS #1 v1.5 signatures. |
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Credit:
The original article can be found at:
http://www.openssl.org/news/secadv_20060905.txt
References:
http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2006-4339
http://www.imc.org/ietf-openpgp/mail-archive/msg14307.html
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Vulnerable Systems:
* OpenSSL versions up to 0.9.7j and 0.9.8b.
If an RSA key with exponent 3 is used it may be possible to forge a PKCS #1 v1.5 signature signed by that key. Implementations may incorrectly verify the certificate if they are not checking for excess data in the RSA exponentiation result of the signature.
Since there are CAs using exponent 3 in wide use, and PKCS #1 v1.5 is used in X.509 certificates, all software that uses OpenSSL to verify X.509 certificates is potentially vulnerable, as well as any other use of PKCS #1 v1.5. This includes software that uses OpenSSL for SSL or TLS.
Resolve:
There are multiple ways to avoid this vulnerability. Any one of the following measures is sufficient.
1. Upgrade the OpenSSL server software.
The vulnerability is resolved in the following versions of OpenSSL:
- in the 0.9.7 branch, version 0.9.7k (or later);
- in the 0.9.8 branch, version 0.9.8c (or later).
OpenSSL 0.9.8c and OpenSSL 0.9.7k are available for download via
HTTP and FTP from the following master locations (you can find the
various FTP mirrors under http://www.openssl.org/source/mirror.html):
* http://www.openssl.org/source/
* ftp://ftp.openssl.org/source/
The distribution file names are:
* openssl-0.9.8c.tar.gz
MD5 checksum: 78454bec556bcb4c45129428a766c886
SHA1 checksum: d0798e5c7c4509d96224136198fa44f7f90e001d
* openssl-0.9.7k.tar.gz
MD5 checksum: be6bba1d67b26eabb48cf1774925416f
SHA1 checksum: 90056b8f5e518edc9f74f66784fbdcfd9b784dd2
The checksums were calculated using the following commands:
openssl md5 openssl-0.9*.tar.gz
openssl sha1 openssl-0.9*.tar.gz
2. If this version upgrade is not an option at the present time, alternatively the following patch may be applied to the OpenSSL source code to resolve the problem. The patch is compatible with the 0.9.6, 0.9.7, 0.9.8, and 0.9.9 branches of OpenSSL.
* http://www.openssl.org/news/patch-CVE-2006-4339.txt
Whether you choose to upgrade to a new version or to apply the patch, make sure to recompile any applications statically linked to OpenSSL libraries.
CVE Information:
CVE-2006-4339
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