cbcvebase.
CVE-2023-41763
published 2023-10-10

CVE-2023-41763: Skype for Business Elevation of Privilege Vulnerability

PriorityP180medium5.3CVSS 3.1
AVNACLPRNUINSUCLINAN
KEVITWEXPLOIT
CISA Known Exploited Vulnerabilitydue 2023-10-31
Exploited in the wild
EPSS
90.35%
99.8th percentile
Skype for Business Elevation of Privilege Vulnerability

Affected

6 ranges
VendorProductVersion rangeFixed in
microsoftskype_for_business_server
microsoftskype_for_business_server
microsoftskype_for_business_server_2015_cu13>= 9319.0 < 6.0.9319.8696.0.9319.869
microsoftskype_for_business_server_2019_cu7>= 2046.0 < 7.0.246.5307.0.246.530
msrcskype_for_business_server_2015_cu13
msrcskype_for_business_server_2019_cu7

Detection & IOCsextracted from sources · hover to see the quote

url/lwa/Webpages/LwaClient.aspx?meeturl=
path/lwa/Webpages/LwaClient.aspx
uaLCS-Server
otherApplication/vnd.microsoft.lync.meeting+xml
snort
alert http $HTTP_SERVERS any -> any any (msg:"ET WEB_SPECIFIC_APPS Possible Skype for Business SSRF Attempt (CVE-2023-41763)"; flow:established,to_server; http.method; content:"GET"; http.accept; content:"Application/vnd.microsoft.lync.meeting+xml"; http.user_agent; content:"LCS-Server"; fast_pattern; reference:url,frycos.github.io/vulns4free/2022/09/26/skype-audit-part2.html; reference:cve,2023-41763; classtype:web-application-attack; sid:2048538; rev:2; metadata:affected_product Skype_For_Business, attack_target Web_Server, created_at 2023_10_11, cve CVE_2023_41763, deployment Internal, deployment SSLDecrypt, performance_impact Low, confidence Low, signature_severity Minor, tag CISA_KEV, updated_at 2024_03_17, reviewed_at 2024_10_02;)
  • The vulnerable endpoint is /lwa/Webpages/LwaClient.aspx; monitor for GET requests to this path with a base64-encoded 'meeturl' parameter, which is the attack vector for the SSRF.
  • Exploit traffic can be identified by the combination of HTTP GET method, Accept header containing 'Application/vnd.microsoft.lync.meeting+xml', and User-Agent containing 'LCS-Server'.
  • Shodan/FOFA queries can identify exposed Skype for Business servers as potential targets: search for html containing 'Skype for Business'.
  • Successful exploitation causes the Skype for Business server to make outbound HTTP requests to attacker-controlled or internal addresses; monitor for unexpected outbound HTTP connections originating from the SfB server process, especially to internal RFC1918 addresses.
  • The vulnerability is pre-authentication (no credentials required); any unauthenticated GET request to LwaClient.aspx with a meeturl parameter should be treated as suspicious.
  • DNS interaction/callback detection (OOB) is a reliable confirmation method for exploitation; monitor for DNS lookups from the SfB server to external domains shortly after requests to LwaClient.aspx.
  • ·The Emergent Threats (ET) Snort rule (sid:2048538) is marked with 'confidence Low' and 'signature_severity Minor', meaning it may produce false positives and should be tuned before use in blocking mode.
  • ·The ET rule requires SSL/TLS decryption to be effective against HTTPS traffic, as indicated by the 'deployment SSLDecrypt' metadata tag.
  • ·The Nuclei template uses out-of-band (interactsh) DNS callback for confirmation; blind SSRF may not produce a visible response in the HTTP body, so passive/inline detection relying solely on response content may miss exploitation.

CVSS provenance

nvdv3.15.3MEDIUMCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
vulncheck5.3MEDIUM
cisa5.3MEDIUM
vendor_msrc5.3MEDIUM
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