{"containers": {"cna": {"affected": [{"product": "PAN-OS", "vendor": "Palo Alto Networks", "versions": [{"status": "affected", "version": "8.1.*"}, {"status": "affected", "version": "9.0.*"}, {"status": "affected", "version": "9.1.*"}, {"status": "affected", "version": "10.0.*"}, {"status": "affected", "version": "10.1.*"}]}], "configurations": [{"lang": "en", "value": "This URL filtering policy evasion situation is only applicable when the following conditions are true:\n\n1. A host in the network is already compromised by a malicious actor.\n\n2. The PAN-OS configuration must have the SSL/TLS Decryption Forward Proxy feature enabled for the specific traffic that the attacker controls.\n\n3. There is no other security device in the chain that performs URL Filtering or can block access to malicious URLs or IP-addresses on the encrypted SSL/TLS traffic."}], "credits": [{"lang": "en", "value": "Palo Alto Networks thanks Morten Marstrander and Matteo Malvica from mnemonic AS for discovering and reporting this issue."}], "datePublic": "2020-08-12T00:00:00", "descriptions": [{"lang": "en", "value": "When SSL/TLS Forward Proxy Decryption mode has been configured to decrypt the web transactions, the PAN-OS URL filtering feature inspects the HTTP Host and URL path headers for policy enforcement on the decrypted HTTPS web transactions but does not consider Server Name Indication (SNI) field within the TLS Client Hello handshake. This allows a compromised host in a protected network to evade any security policy that uses URL filtering on a firewall configured with SSL Decryption in the Forward Proxy mode. A malicious actor can then use this technique to evade detection of communication on the TLS handshake phase between a compromised host and a remote malicious server. This technique does not increase the risk of a host being compromised in the network. It does not impact the confidentiality or availability of a firewall. This is considered to have a low impact on the integrity of the firewall because the firewall fails to enforce a policy on certain traffic that should have been blocked. This issue does not impact the URL filtering policy enforcement on clear text or encrypted web transactions. This technique can be used only after a malicious actor has compromised a host in the protected network and the TLS/SSL Decryption feature is enabled for the traffic that the attacker controls. Palo Alto Networks is not aware of any malware that uses this technique to exfiltrate data. This issue is applicable to all current versions of PAN-OS. This issue does not impact Panorama or WF-500 appliances."}], "exploits": [{"lang": "en", "value": "Palo Alto Networks is not aware of any malware that uses this technique to exfiltrate data."}], "metrics": [{"cvssV3_1": {"attackComplexity": "HIGH", "attackVector": "NETWORK", "availabilityImpact": "NONE", "baseScore": 3, "baseSeverity": "LOW", "confidentialityImpact": "NONE", "integrityImpact": "LOW", "privilegesRequired": "HIGH", "scope": "CHANGED", "userInteraction": "NONE", "vectorString": "CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:C/C:N/I:L/A:N", "version": "3.1"}}], "problemTypes": [{"descriptions": [{"cweId": "CWE-20", "description": "CWE-20 Improper Input Validation", "lang": "en", "type": "CWE"}]}], "providerMetadata": {"dateUpdated": "2021-06-10T12:33:06", "orgId": "d6c1279f-00f6-4ef7-9217-f89ffe703ec0", "shortName": "palo_alto"}, "references": [{"tags": ["x_refsource_MISC"], "url": "https://security.paloaltonetworks.com/CVE-2020-2035"}, {"tags": ["x_refsource_MISC"], "url": "https://www.mnemonic.no/blog/introducing-snicat/"}], "solutions": [{"lang": "en", "value": "Palo Alto Networks is currently working to improve our inspection engines by adding a URL filtering policy check on both the TLS SNI field and the HTTP Host and URL headers for decrypted HTTPS transactions.\n\nApply any of the workarounds to completely mitigate the risk of evasion.\n\nThere are currently no PAN-OS updates available for this issue."}], "source": {"defect": ["PAN-140086"], "discovery": "EXTERNAL"}, "timeline": [{"lang": "en", "time": "2020-08-12T00:00:00", "value": "Initial publication"}, {"lang": "en", "time": "2021-03-03T00:00:00", "value": "Added clarification that Panorama and WF-500 appliances are not impacted"}, {"lang": "en", "time": "2021-06-09T00:00:00", "value": "Updated impacted versions to include PAN-OS 10.1"}], "title": "PAN-OS: URL filtering policy is not enforced on TLS handshakes for decrypted HTTPS sessions", "workarounds": [{"lang": "en", "value": "Customers concerned about the risk described in this advisory are encouraged to review the KB article https://knowledgebase.paloaltonetworks.com/KCSArticleDetail?id=kA14u0000008V4J for more information on background and mitigation options. To enforce URL filtering policy on TLS handshakes for decrypted HTTPS sessions, we suggest you use any one of the following workarounds:\n\n1. Route outbound traffic between two virtual systems (vsys) on PAN-OS firewalls that have vsys capability and perform URL Filtering on one vsys and perform SSL/TLS Decryption on the other vsys.\n\n2. Add two additional Security Zones and route outbound traffic between the two zones so that you can apply both \"Decrypt\" and \"No Decrypt\" Decryption policy rules. For example, configure your next-generation firewall so that traffic travels from the Inside zone to the Internal-DMZ zone where you applied a \u201cNo Decrypt\u201d rule along with URL Filtering and then the traffic passes to the External-DMZ zone and from External-DMZ to the Internet zone where you applied a \"Decrypt\" rule. Be aware that this workaround configuration may significantly increase the load on your firewall.\n\n3. 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There are additional risks associated with this action."}], "x_generator": {"engine": "Vulnogram 0.0.9"}, "x_legacyV4Record": {"CVE_data_meta": {"ASSIGNER": "psirt@paloaltonetworks.com", "DATE_PUBLIC": "2020-08-12T16:00:00.000Z", "ID": "CVE-2020-2035", "STATE": "PUBLIC", "TITLE": "PAN-OS: URL filtering policy is not enforced on TLS handshakes for decrypted HTTPS sessions"}, "affects": {"vendor": {"vendor_data": [{"product": {"product_data": [{"product_name": "PAN-OS", "version": {"version_data": [{"version_affected": "=", "version_name": "8.1", "version_value": "8.1.*"}, {"version_affected": "=", "version_name": "9.0", "version_value": "9.0.*"}, {"version_affected": "=", "version_name": "9.1", "version_value": "9.1.*"}, {"version_affected": "=", "version_name": "10.0", "version_value": "10.0.*"}, {"version_affected": "=", "version_name": "10.1", "version_value": "10.1.*"}]}}]}, "vendor_name": "Palo Alto Networks"}]}}, "configuration": [{"lang": "en", "value": "This URL filtering policy evasion situation is only applicable when the following conditions are true:\n\n1. 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{"configurations": [{"nodes": [{"cpeMatch": [{"criteria": "cpe:2.3:o:paloaltonetworks:pan-os:*:*:*:*:*:*:*:*", "matchCriteriaId": "7DEC9117-FD67-4AC1-AECC-A264B79F403E", "vulnerable": true}], "negate": false, "operator": "OR"}]}], "cveTags": [], "descriptions": [{"lang": "en", "value": "When SSL/TLS Forward Proxy Decryption mode has been configured to decrypt the web transactions, the PAN-OS URL filtering feature inspects the HTTP Host and URL path headers for policy enforcement on the decrypted HTTPS web transactions but does not consider Server Name Indication (SNI) field within the TLS Client Hello handshake. This allows a compromised host in a protected network to evade any security policy that uses URL filtering on a firewall configured with SSL Decryption in the Forward Proxy mode. A malicious actor can then use this technique to evade detection of communication on the TLS handshake phase between a compromised host and a remote malicious server. This technique does not increase the risk of a host being compromised in the network. It does not impact the confidentiality or availability of a firewall. This is considered to have a low impact on the integrity of the firewall because the firewall fails to enforce a policy on certain traffic that should have been blocked. This issue does not impact the URL filtering policy enforcement on clear text or encrypted web transactions. This technique can be used only after a malicious actor has compromised a host in the protected network and the TLS/SSL Decryption feature is enabled for the traffic that the attacker controls. Palo Alto Networks is not aware of any malware that uses this technique to exfiltrate data. This issue is applicable to all current versions of PAN-OS. This issue does not impact Panorama or WF-500 appliances."}, {"lang": "es", "value": "Cuando se ha configurado el modo de descifrado SSL/TLS Forward Proxy para descifrar las transacciones web, la funci\u00f3n de filtrado de URL de PAN-OS inspecciona las cabeceras HTTP Host y URL Path para la aplicaci\u00f3n de pol\u00edticas en las transacciones web HTTPS descifradas, pero no tiene en cuenta el campo Server Name Indication (SNI) dentro del handshake TLS Client Hello. Esto permite que un host comprometido en una red protegida evada cualquier pol\u00edtica de seguridad que utilice el filtrado de URL en un cortafuegos configurado con descifrado SSL en el modo de proxy de reenv\u00edo. Un actor malicioso puede entonces utilizar esta t\u00e9cnica para evadir la detecci\u00f3n de la comunicaci\u00f3n en la fase de handshake TLS entre un host comprometido y un servidor remoto malicioso. Esta t\u00e9cnica no aumenta el riesgo de que un host se vea comprometido en la red. No afecta a la confidencialidad ni a la disponibilidad de un cortafuegos. Se considera que tiene un impacto bajo en la integridad del cortafuegos porque \u00e9ste no aplica una pol\u00edtica sobre cierto tr\u00e1fico que deber\u00eda haber sido bloqueado. Este problema no afecta a la aplicaci\u00f3n de la pol\u00edtica de filtrado de URL en las transacciones web de texto claro o cifrado. Esta t\u00e9cnica s\u00f3lo puede utilizarse despu\u00e9s de que un actor malicioso haya comprometido un host en la red protegida y la funci\u00f3n de descifrado TLS/SSL est\u00e9 habilitada para el tr\u00e1fico que el atacante controla. Palo Alto Networks no tiene conocimiento de ning\u00fan malware que utilice esta t\u00e9cnica para exfiltrar datos. Este problema es aplicable a todas las versiones actuales de PAN-OS. 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