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AUSCERT External Security Bulletin Redistribution
ESB-2017.3182.4
TLS vulnerability discovered in Cisco products (ROBOT)
22 December 2017
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AusCERT Security Bulletin Summary
---------------------------------
Product: Cisco products
Publisher: Cisco Systems
Operating System: Network Appliance
Impact/Access: Access Privileged Data -- Remote/Unauthenticated
Resolution: Mitigation
CVE Names: CVE-2017-17428
Original Bulletin:
https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20171212-bleichenbacher
https://robotattack.org
Revision History: December 22 2017: Updated source text: affected products, vulnerable products, confirmed not vulnerable, & details
December 18 2017: Updated source text with known non-vulnerable products
December 15 2017: Updated source text with more detail on vulnerable appliances/intended fixes
December 13 2017: Initial Release
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Bleichenbacher Attack on TLS Affecting Cisco Products: December 2017
Severity: Medium
Advisory ID: cisco-sa-20171212-bleichenbacher
First Published: 2017 December 12 15:45 GMT
Last Updated: 2017 December 21 23:17 GMT
Version 1.3: Interim
Workarounds: Yes
Cisco Bug IDs: CSCvg74693 CSCvg97652 CSCvh10981 CSCvg74693 CSCvg97652
CSCvh10981 CSCvh25064 CVE-2017-12373 CVE-2017-17428 CWE-200
CVSS Score: Base 5.3
CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N/E:X/RL:X/RC:X
CVE-2017-12373
CVE-2017-17428
CWE-200
Summary
* 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 will release 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
Affected Products
* Cisco investigated its product line to determine which products may be
affected by these vulnerabilities and the impact on each affected product.
Refer to the "Vulnerable Products" and "Products Confirmed Not Vulnerable"
sections of this advisory for information about whether a product is
affected.
The "Vulnerable Products" section includes Cisco bug IDs for each affected
product. The bugs are accessible through the Cisco Bug Search Tool and
contain additional platform-specific information, including workarounds (if
available) and fixed software releases.
Vulnerable Products
The following table lists Cisco products that are affected by one or more
of the vulnerabilities that are described in this advisory:
Product Cisco Bug Fixed Release Availability
ID
Cisco Cloud Hosted Services
Cisco WebEx Business Suite (including Remediation currently
Meeting Center, Training Center, CSCvh10981 planned to be completed by
Event Center, Support Center) January 15th, 2018.
Remediation currently
Cisco WebEx Meetings CSCvh10981 planned to be completed by
January 15th, 2018.
Remediation currently
Cisco WebEx Messenger CSCvh25064 planned to be completed by
January 15th, 2018.
Network Application, Service, and Acceleration
Cisco ACE 4710 Application Control CSCvg74693 No fix will be provided
Engine Appliance for this product. ^1
Cisco ACE30 Application Control CSCvg74693 No fix will be provided
Engine Module for this product. ^2
Network and Content Security Devices
Cisco Adaptive Security Appliance A fix is planned for
(ASA) - ASA 5505, 5510, 5520, 5540, CSCvg97652 9.1.7.x and 9.2.4.x
and 5550 releases. ETA: TBD
^1 Cisco ACE 4710 Application Control Engine Appliance entered the
end-of-life cycle on July 26, 2013. For reference, see the End-of-Sale and
End-of-Life Announcement.
^2 Cisco ACE30 Application Control Engine Module entered the end-of-life
cycle on July 26, 2013. For reference, see the End-of-Sale and End-of-Life
Announcement.
Products Confirmed Not Vulnerable
No other Cisco products are currently known to be affected by these
vulnerabilities.
Cisco has confirmed that these vulnerabilities do not affect the following
products:
Cisco Cloud Hosted Services
+ Cisco Cloud Web Security (CWS)
+ Cisco Spark
+ Cisco Umbrella
Network Application, Service, and Acceleration
+ Cisco Wide Area Application Services (WAAS)
Network and Content Security Devices
+ Cisco Adaptive Security Appliance (ASA) - all models not listed in the
Vulnerable Products section
+ Cisco ASA Next-Generation Firewall Services
+ Cisco Content Security Management Appliance (SMA)
+ Cisco Email Security Appliance (ESA)
+ Cisco Firepower 2100 Series
+ Cisco Firepower 4100 Series
+ Cisco Firepower 9300 Security Appliance
+ Cisco Identity Services Engine (ISE)
+ Cisco Web Security Appliance (WSA)
Routing and Switching - Enterprise and Service Provider
+ Cisco VPN Internal Service Module for ISR (VPN ISM)
Details
* 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:
SSL SDK Bleichenbacher Attack Information Disclosure Vulnerability
A vulnerability in the TLS protocol implementation on the crypto hardware
SSL Software Development Kit (SDK) 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.
Workarounds
* 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 ID, which is available from the Cisco Bug Search Tool.
Fixed Software
* 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.
Exploitation and Public Announcements
* The Cisco Product Security Incident Response Team (PSIRT) is not aware of
any malicious use of the vulnerabilities that are described in this
advisory.
Source
* Cisco would like to thank Hanno Bock, Juraj Somorovsky of Ruhr-University
Bochum/Hackmanit GmbH, Craig Young of Tripwire VERT, and Dirk Wetter of
testssl.sh/Dr. Wetter IT-Consulting for reporting these vulnerabilities.
URL
* https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/
cisco-sa-20171212-bleichenbacher
Revision History
*
+-----------------------------------------------------------------------------+
| Version | Description | Section | Status | Date |
|---------+--------------------+-----------------+---------+------------------|
| | Updated | | | |
| | information for | Affected | | |
| | vulnerable and | Products, | | |
| | nonvulnerable | Vulnerable | | |
| 1.3 | products and | Products, | Interim | 2017-December-21 |
| | products under | Products | | |
| | investigation. | Confirmed Not | | |
| | Modified | Vulnerable, | | |
| | CVE-2017-12373 | Details | | |
| | description. | | | |
|---------+--------------------+-----------------+---------+------------------|
| | Updated | Products | | |
| 1.2 | information for | Confirmed Not | Interim | 2017-December-15 |
| | nonvulnerable | Vulnerable | | |
| | products. | | | |
|---------+--------------------+-----------------+---------+------------------|
| | Updated | Vulnerable | | |
| | information for | Products, | | |
| | vulnerable and | Products | | |
| | nonvulnerable | Confirmed Not | | |
| 1.1 | products and | Vulnerable, | Interim | 2017-December-13 |
| | products under | Products Under | | |
| | investigation. | Investigation, | | |
| | Added | Details | | |
| | CVE-2017-12373. | | | |
|---------+--------------------+-----------------+---------+------------------|
| 1.0 | Initial public | ? | Interim | 2017-December-12 |
| | release. | | | |
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