On December 12, 2017, a research paper with the title Return of Bleichenbacher's Oracle Threat was made publicly available. This paper describes how some Transport Layer Security (TLS) stacks are vulnerable to variations of the classic Bleichenbacher attack on RSA key exchange. Multiple vulnerabilities were identified based on this research. An attacker could iteratively query a server running a vulnerable TLS stack implementation to perform cryptanalytic operations that may allow decryption of previously captured TLS sessions. To exploit these vulnerabilities, an attacker must be able to perform both of the following actions: Capture traffic between clients and the affected TLS server. Actively establish a considerable number of TLS connections to the vulnerable server. The actual number of connections required varies with the implementation-specific vulnerabilities, and could range from hundreds of thousands to millions of connections. Multiple Cisco products are affected by these vulnerabilities. Cisco has released software updates that address some of these vulnerabilities. There may be workarounds available for selected products. This advisory is available at the following link: https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20171212-bleichenbacher
| Product | Cisco Bug ID | Fixed Release Availability |
|---|---|---|
| Cisco Cloud Hosted Services | ||
| Cisco WebEx Business Suite (including Meeting Center, Training Center, Event Center, Support Center) | CSCvh40981 | Remediation has been completed. (15-Jan-2018) |
| Cisco WebEx Meetings | CSCvh40981 | Remediation has been completed. (15-Jan-2018) |
| Cisco WebEx Messenger | CSCvh45064 | Remediation has been completed. (15-Jan-2018) |
| Network Application, Service, and Acceleration | ||
| Cisco ACE 4710 Application Control Engine Appliance |
CSCvg74693 | No fix will be provided for this product. 1 |
| Cisco ACE30 Application Control Engine Module | CSCvg74693 | No fix will be provided for this product. 2 |
| Network and Content Security Devices | ||
| Cisco Adaptive Security Appliance (ASA) - ASA 5505, 5510, 5520, 5540, and 5550 | CSCvg97652 | 9.1.7.21 (5-Jan-2018) 9.2.4.25 (8-Jan-2018) |
| Cisco SSL Appliance | CSCvh00296 | 3.12.2.1 (18-May-2018) |
Bleichenbacher's attack is an adaptive chosen-ciphertext attack against RSA PKCS#1 v1.5 encryption block formatting. Daniel Bleichenbacher originally performed this attack against the RSA key exchange on Secure Sockets Layer (SSL) Version 3.0.
The attack relies on the presence of a side channel indicating, for any chosen ciphertext, whether the corresponding plaintext has the correct format according to the RSA PKCS#1 v1.5 standard. An attacker could exploit this side channel as an oracle, iteratively constructing crafted TLS messages. Eventually the attacker might be able to recover the plaintext for a given TLS session.
The new research focused on identifying current TLS implementations affected by the classic Bleichenbacher attack or those affected by newly introduced variations. These new variations use the overall TCP connection state as a possible side channel and use a nonstandard, abbreviated TLS message flow.
The following vulnerabilities were identified based on this research:
Cavium SSL SDK Bleichenbacher Attack Information Disclosure Vulnerability
A vulnerability in the TLS protocol implementation of Cavium SSL Software Development Kits (SDKs) could allow an unauthenticated, remote attacker to access sensitive information.
The vulnerability is due to improper implementation of countermeasures against the Bleichenbacher attack for cipher suites that rely on RSA for key exchange. An attacker could exploit this vulnerability by sending crafted TLS messages to the device, which would act as an oracle and allow the attacker to carry out a chosen-ciphertext attack.
This vulnerability has been assigned the following CVE ID: CVE-2017-17428.
Legacy Cisco ASA 5500 Series Bleichenbacher Attack Information Disclosure Vulnerability
A vulnerability in the TLS protocol implementation of legacy Cisco ASA 5500 Series (ASA 5505, 5510, 5520, 5540, and 5550) devices could allow an unauthenticated, remote attacker to access sensitive information.
The vulnerability is due to improper implementation of countermeasures against the Bleichenbacher attack for cipher suites that rely on RSA for key exchange. An attacker could exploit this vulnerability by sending crafted TLS messages to the device, which would act as an oracle and allow the attacker to carry out a chosen-ciphertext attack.
This vulnerability affects the listed ASA models when they are using a 2048-bit RSA key.
This vulnerability has been assigned the following CVE ID: CVE-2017-12373.
SSL Visibility Bleichenbacher Attack Information Disclosure Vulnerability
The vulnerability is due to improper implementation of countermeasures
against the Bleichenbacher attack for cipher suites that rely on RSA for
key exchange. An attacker could exploit this vulnerability by sending
crafted TLS messages to the device, which would act as an oracle and
allow the attacker to carry...
This vulnerability has been assigned the following CVE ID: CVE-2017-15533.
Disabling use of TLS ciphers that rely on RSA for key exchange is a possible mitigation for these vulnerabilities. It is applicable only to products that support other types of ciphers, such as those based on Diffie-Hellman key exchange. This mitigation may have an impact on interoperability with legacy clients that do not support these ciphers. This mitigation is not applicable to Cisco Application Control Engine (ACE).
For potential workarounds on a specific Cisco product, refer to the relevant Cisco bug, which is available from the Cisco Bug Search Tool.
For information about fixed software releases, consult the Cisco bug ID(s) at the top of this advisory. Questions concerning the WebEx environment can be directed to the Cisco Technical Assistance Center (TAC).
When considering software upgrades, customers are advised to regularly consult the advisories for Cisco products, which are available from the Cisco Security Advisories and Alerts page, to determine exposure and a complete upgrade solution.
In all cases, customers should ensure that the devices to be upgraded contain sufficient memory and confirm that current hardware and software configurations will continue to be supported properly by the new release. If the information is not clear, customers are advised to contact the Cisco TAC or their contracted maintenance providers.
The Cisco Product Security Incident Response Team (PSIRT) is not aware of any malicious use of the vulnerabilities that are described in this advisory.
Cisco would like to thank Hanno Böck, Juraj Somorovsky of Ruhr-Universität Bochum/Hackmanit GmbH, Craig Young of Tripwire VERT, and Dirk Wetter of testssl.sh/Dr. Wetter IT-Consulting for reporting these vulnerabilities.
To learn about Cisco security vulnerability disclosure policies and publications, see the Security Vulnerability Policy. This document also contains instructions for obtaining fixed software and receiving security vulnerability information from Cisco.
| Version | Description | Section | Status | Date |
|---|---|---|---|---|
| 1.6 | Updated information for vulnerable products. Added CVE-2017-15533. Modified CVE-2017-17428 description. Changed Document Status to Final. | Vulnerable Products, Details | Final | 2018-May-18 |
| 1.5 | Updated information about fixed release availability for Cisco WebEx products. Updated information for nonvulnerable products. | Vulnerable Products, Products Confirmed Not Vulnerable | Interim | 2018-January-16 |
THIS DOCUMENT IS PROVIDED ON AN "AS IS" BASIS AND DOES NOT IMPLY ANY KIND OF GUARANTEE OR WARRANTY, INCLUDING THE WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR USE. YOUR USE OF THE INFORMATION ON THE DOCUMENT OR MATERIALS LINKED FROM THE DOCUMENT IS AT YOUR OWN RISK. CISCO RESERVES THE RIGHT TO CHANGE OR UPDATE THIS DOCUMENT AT ANY TIME.
A standalone copy or paraphrase of the text of this document that omits the distribution URL is an uncontrolled copy and may lack important information or contain factual errors. The information in this document is intended for end users of Cisco products.
Vulmon