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-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 =========================================================================== AUSCERT External Security Bulletin Redistribution ESB-2023.6365 Cisco Adaptive Security Appliance Software and Firepower Threat Defense Software AnyConnect SSL/TLS VPN Denial of Service Vulnerability 2 November 2023 =========================================================================== AusCERT Security Bulletin Summary --------------------------------- Product: Cisco Adaptive Security Appliance Software Firepower Threat Defense Software Publisher: Cisco Systems Operating System: Cisco Resolution: Patch/Upgrade CVE Names: CVE-2023-20042 Original Bulletin: https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-asaftd-ssl-dos-kxG8mpUA Comment: CVSS (Max): 6.8 CVE-2023-20042 (CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:N/A:H) CVSS Source: Cisco Systems Calculator: https://www.first.org/cvss/calculator/3.1#CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:N/I:N/A:H - --------------------------BEGIN INCLUDED TEXT-------------------- Cisco Adaptive Security Appliance Software and Firepower Threat Defense Software AnyConnect SSL/TLS VPN Denial of Service Vulnerability Priority: Medium Advisory ID: cisco-sa-asaftd-ssl-dos-kxG8mpUA First Published: 2023 November 1 16:00 GMT Version 1.0: Final Workarounds: No workarounds available Cisco Bug IDs: CSCwd62859 CVE Names: CVE-2023-20042 Summary o A vulnerability in the AnyConnect SSL VPN feature of Cisco Adaptive Security Appliance (ASA) Software and Cisco Firepower Threat Defense (FTD) Software could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on an affected device. This vulnerability is due to an implementation error within the SSL/TLS session handling process that can prevent the release of a session handler under specific conditions. An attacker could exploit this vulnerability by sending crafted SSL/TLS traffic to an affected device, increasing the probability of session handler leaks. A successful exploit could allow the attacker to eventually deplete the available session handler pool, preventing new sessions from being established and causing a DoS condition. Cisco has released software updates that address this vulnerability. There are no workarounds that address this vulnerability. This advisory is available at the following link: https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-asaftd-ssl-dos-kxG8mpUA This advisory is part of the November 2023 release of the Cisco ASA, FTD, and FMC Security Advisory Bundled publication. For a complete list of the advisories and links to them, see Cisco Event Response: November 2023 Semiannual Cisco ASA, FMC, and FTD Software Security Advisory Bundled Publication . Affected Products o Vulnerable Products At the time of publication, this vulnerability affected Cisco ASA Software and FTD Software that was configured for AnyConnect SSL/TLS VPN connections. For information about which Cisco software releases are vulnerable, see the Fixed Software section of this advisory. Products Confirmed Not Vulnerable Only products listed in the Vulnerable Products section of this advisory are known to be affected by this vulnerability. Indicators of Compromise o It is possible to detect the presence of leaked session handlers using the command show SSL objects . An abnormal and increasing number in the SSL: active counter indicates that sessions are leaking. ASA/FTD# show SSL objects SSL object statistics: SSL: active: 29778, peak: 29793, total: 2507224 SSL_CTX: active: 4, peak: 6, total: 1704772 SSL_SESSION: active: 30548, peak: 30796, total: 1076386 X509: active: 15, peak: 16, total: 3036 X509_STORE: active: 6, peak: 9, total: 1704819 X509_STORE_CTX: active: 0, peak: 3, total: 796310 DH: active: 2, peak: 8, total: 2035 EC_KEY: active: 12, peak: 14, total: 480347 RSA: active: 16, peak: 18, total: 1529 ENGINE: active: 2, peak: 2, total: 2 BIO: active: 52367, peak: 52385, total: 5642732 DRBG: active: 18446744073709541998, peak: 0, total: 0 103132 active objects, 13919192 total objects Workarounds o There are no workarounds that address this vulnerability. Fixed Software o When considering software upgrades , customers are advised to regularly consult the advisories for Cisco products, which are available from the Cisco Security Advisories 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 Technical Assistance Center (TAC) or their contracted maintenance providers. Cisco ASA, FMC, and FTD Software To help customers determine their exposure to vulnerabilities in Cisco ASA, FMC, and FTD Software, Cisco provides the Cisco Software Checker . This tool identifies any Cisco security advisories that impact a specific software release and the earliest release that fixes the vulnerabilities that are described in each advisory ("First Fixed"). If applicable, the tool also returns the earliest release that fixes all the vulnerabilities that are described in all the advisories that the Software Checker identifies ("Combined First Fixed"). To use the tool, go to the Cisco Software Checker page and follow the instructions. Alternatively, use the following form to search for vulnerabilities that affect a specific software release. To use the form, follow these steps: 1. Choose which advisories the tool will search-all advisories, only advisories with a Critical or High Security Impact Rating (SIR) , or only this advisory. 2. Choose the appropriate software. 3. Choose the appropriate platform. 4. Enter a release number-for example, 9.16.2.11 for Cisco ASA Software or 6.6.7 for Cisco FTD Software. 5. Click Check . [2 ] [ ] [Critical,High,Medium] [Only this advisory ] [Cisco ASA Software] [Any Platform ] [ ] [Check] For instructions on upgrading your FTD device, see Cisco Firepower Management Center Upgrade Guide . Exploitation and Public Announcements o The Cisco PSIRT is not aware of any public announcements or malicious use of the vulnerability that is described in this advisory. Source o This vulnerability was found during the resolution of a Cisco TAC support case. Cisco Security Vulnerability Policy o 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. Subscribe to Cisco Security Notifications o Subscribe Related to This Advisory o Cisco Event Response: November 2023 Cisco ASA, FMC, and FTD Software Security Advisory Bundled Publication URL o https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-asaftd-ssl-dos-kxG8mpUA Revision History o +----------+---------------------------+----------+--------+--------------+ | Version | Description | Section | Status | Date | +----------+---------------------------+----------+--------+--------------+ | 1.0 | Initial public release. | - | Final | 2023-NOV-01 | +----------+---------------------------+----------+--------+--------------+ Legal Disclaimer o 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. 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On call after hours for member emergencies only. =========================================================================== -----BEGIN PGP SIGNATURE----- Comment: https://auscert.org.au/gpg-key/ iQIVAwUBZUMMIskNZI30y1K9AQhAww/+NE4/UZZZbBRcQ1sm9Ht1rPE+UOLibtG8 67pyfkImATFDzLkVnXJ4//R7qPhan1mELUPjJgZnlEKXTBbmCa2ibe5FSUXrlt7G by9NdcIisYrgAyDkVVX/LhwUsXm/ejl5keP6ToXxOkUvzEs9WqxQqqdq+jd6tyP1 vS41GIhC7EiunCs7f8Cmivm7i04VN3JsdCcri2KF7+iZGSoUXTn1gGDeS+3w5V6z OLhI8ShixZEGKrotX2/AavVL9vl3cSaXZWa1cn4FEUZCKdfBJ+Qdy9QI4ajDzylA inlHExMfLTPovjaGom8BCXjx5jxJleYtgbJN2Yb/Bt+9gU/iB+twareLoKMOPiUk 24ifC7hdBsVSwvd1yANzLT0kR3aIHrOMzfwaVUSb6eccqA7iozyZGeS2wsiqsGG7 LnVtVL/WzMpfx0FLMbjzIs4U0Gh5KNq28JvkqpzTm5fRhwKN0kk9JkAxMxTsS89R MSgHI6mPlvXWIGbxLOVxMdlTwaJ8aVEc/ZTEfXA0Fw0b9VynfMGocF2vt/XTurs4 4As3ZW1nX288m2scFOEasEZzpEtpal/q4RNCwGFqjj5b+71MT4xmBfchceR0LM33 jofhYaQI2LwQxRcL7uNRyR6yHdoafVqy1TPaP4ZM76qgP8a5LYDywBmHVkj3ZIOa FnrOcv8QLSE= =kro3 -----END PGP SIGNATURE-----