Kemp Load Balancer WAF 7.2.40 Bypass
Posted on 15 December 2017
1. ADVISORY SUMMARY Kemp Load Balancers - Module Application Firewall Pack (AFP) - Web Application Firewall (WAF) does not inspect HTTP POST data Risk: high Application: Kemp Load Balancers - Module Application Firewall Pack (AFP) Versions Affected: 7.1.30 (Nov 2015) to 7.2.40 (Oct 2017) // Older versions are probably affected too, but they were not checked Vendor: KEMP Technologies Vendor URL: https://kemptechnologies.com/ Sent to vendor: 16.10.2017 Vendor response: Acknowledge 17.10.2017, Fix in PreRelease 30.11.2017 Published fixed Release by vendor: 06.12.2017 Date of Public Advisory: 11.12.2017 Reference: Kemp Case #75046 Advisory URL: https://www.pallas.com/advisories/cve_2017_15524_kemp_afp_waf_bug_on_post_data Author: Tim Kretschmann (Pallas GmbH) Version and State of report: 1.0 (11.12.2017) - published 2. VULNERABILITY INFORMATION Web Application Firewall does not inspect HTTP POST data Remotely Exploitable: Yes Locally Exploitable: No CVE: CVE-2017-15524 CVSS Base Score v2: 10 / 10 CVSS Base Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:N 3. VULNERABILITY DESCRIPTION Kemp Load Balancer Module Application Firewall Pack (AFP) provides Web Application Firewall functionality. In the tested versiona only web attacks at URL arguments were checked and were successful detected/blocked. Attacks at arguments in the payload of HTTP POST Requests were NOT checked and were NOT detected/blocked. Any attacks based on HTTP POST by using the Payload to transfer the attack vector will bypass the Web Applications Firewall of Kemp. 4. SOLUTIONS AND WORKAROUNDS Update to Release 7.2.40.1 (Nov 2017) No possible workaround before 7.2.40.1 5. AUTHOR Tim Kretschmann (Pallas GmbH) 6. TECHNICAL DESCRIPTION / PROOF OF CONCEPT (PoC) Settings WAF on KEMP Load Balancer inside Virtual Service of Virtal Host Area WAF Options Web Application Firewall Enabled: On Default Operation: Block Mode Audit mode: Audit Relevant Inspect HTML POST Request Content: On - Disable JSON Parser: Off - Disable XML Parser: Off Process Responses: Off Test-RuleSet: SecRequestBodyAccess On SecRule ARGS_POST:ptest attack123 "phase:2,id:8000,block,msg:'test 8000',log,auditlog" SecRule ARGS_POST:ptest attack123 "phase:2,id:8001,deny,msg:'test 8001',log,auditlog" SecRule ARGS_POST:ptest attack123 "phase:2,id:8002,drop,msg:'test 8002',log,auditlog" SecRule ARGS_POST:ptest attack123 "phase:1,id:8003,block,msg:'test 8003',log,auditlog" SecRule ARGS_POST:ptest attack123 "phase:1,id:8004,deny,msg:'test 8004',log,auditlog" SecRule ARGS_POST:ptest attack123 "phase:1,id:8005,drop,msg:'test 8005',log,auditlog" SecRule ARGS:ptest attack123 "phase:2,id:8010,block,msg:'test 8010',log,auditlog" SecRule ARGS:ptest attack123 "phase:2,id:8011,deny,msg:'test 8011',log,auditlog" SecRule ARGS:ptest attack123 "phase:2,id:8012,drop,msg:'test 8012',log,auditlog" SecRule ARGS:ptest attack123 "phase:1,id:8013,block,msg:'test 8013',log,auditlog" SecRule ARGS:ptest attack123 "phase:1,id:8014,deny,msg:'test 8014',log,auditlog" SecRule ARGS:ptest attack123 "phase:1,id:8015,drop,msg:'test 8015',log,auditlog" Proof-of-Concept: pentest@testpc:~$ curl -X GET "http://www.website.tld/cms/login.xhtml?ptest=attack123" <html><head><title>403 Forbidden</title></head><body>Access denied</body> --> Is blocked. Okay. pentest@testpc:~$ curl -X POST "http://www.website.tld/cms/login.xhtml?ptest=attack123" -d "xx=1" <html><head><title>403 Forbidden</title></head><body>Access denied</body> --> Is blocked. Okay. pentest@testpc:~$ curl -X POST "http://www.website.tld/cms/login.xhtml" -H "Content-Type: application/x-www-form-urlencoded" -d "ptest=attack123" -s <?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> Content of website !! --> No Block/Drop/Deny on POST Attacks !! 7. TIMELINE 16.10.2017 - Open Ticket at Kemp #75046 17.10.2017 - Kemp acknowledged the bug 30.11.2017 Kemp offered PreRelease 7.2.40.1.15841.RELEASE.20171129-1431-PATCH-64-MULTICORE to Pallas 06.12.2017 Kemp published Release 7.2.40.1 (see https://kemptechnologies.com/software-release-notes/ - PD-10249) 11.12.2017 Pallas published Advisory 8. ABOUT PALLAS GMBH Pallas provides security consulting, pentesting, managed security services and hosting services with focus on security. Adress: Pallas GmbH, Hermuelheimer Strasse 8a, 50321 Bruehl, GERMANY Phone: 0049.2232.18960 Fax: 0049.2232.198629 Web: https://www.pallas.com/
