CVE-2018-13415

published 2018-08-13

CVE-2018-13415: In Plex Media Server 1.13.2.5154, the XML parsing engine for SSDP/UPnP functionality is vulnerable to an XML External Entity Processing (XXE) attack. Remote…

Priority P2 76 critical 9.8 CVSS 3.0

AV N AC L PR N UI N S U C H I H A H

EXPLOIT

In Plex Media Server 1.13.2.5154, the XML parsing engine for SSDP/UPnP functionality is vulnerable to an XML External Entity Processing (XXE) attack. Remote, unauthenticated attackers can use this vulnerability to: (1) Access arbitrary files from the filesystem with the same permission as the user account running Plex, (2) Initiate SMB connections to capture a NetNTLM challenge/response and crack to cleartext password, or (3) Initiate SMB connections to relay a NetNTLM challenge/response and achieve Remote Command Execution in Windows domains.

Affected

1 ranges

Vendor	Product	Version range	Fixed in
plex	media_server	—	—

Detection & IOCs extracted from sources · hover to see the quote

url https://gitlab.com/initstring/evil-ssdp↗

port 1900/udp↗

ip 239.255.255.250↗

path /ssdp/device-desc.xml↗

path /ssdp/data.dtd↗

port 445/tcp↗

ua DVBLink↗

version Plex Media Server 1.13.2.5154↗

• → Monitor for outbound SMB connections (port 445) originating from the Plex Media Server process — this is anomalous and indicates XXE-triggered NTLM relay/capture activity. ↗
• → Detect HTTP GET requests to paths matching /ssdp/device-desc.xml and /ssdp/data.dtd on attacker-controlled servers; these are the XXE payload delivery paths used in exploitation. ↗
• → Alert on HTTP GET requests containing the pattern /?exfiltrated= in the URI, which indicates successful out-of-band XXE file exfiltration from Plex. ↗
• → Monitor SSDP traffic (UDP 239.255.255.250:1900) for M-SEARCH responses that include a Device Descriptor URL pointing to an external or non-local host, which is the initial XXE trigger vector. ↗
• → Inspect XML content fetched by Plex over HTTP for DOCTYPE declarations containing ENTITY tags referencing SMB (file://) or HTTP URIs — presence of these in SSDP device descriptors is the XXE payload signature. ↗
• → Look for the [XXE VULN!!!!] log pattern or equivalent: a User-Agent of 'None' making requests to /ssdp/device-desc.xml, which is the fingerprint of Plex's libxml2 XXE callback. ↗

• · The attack is limited to attackers on the same LAN as the Plex server, as it requires responding to SSDP UDP multicast traffic on the local network segment. ↗
• · File exfiltration via XXE (POC 2) is limited to single-line files with no whitespace; multi-line or whitespace-containing files cannot be reliably exfiltrated with this technique. ↗
• · The vulnerability is exploited automatically upon Plex restart — no user interaction beyond restarting the service is required, making it a zero-click attack on the LAN. ↗
• · The XXE is processed by libxml2 within Plex's SSDP/UPnP component; the affected component and library should be the focus of patching and version tracking. ↗

CVSS provenance

nvd v3.0 9.8 CRITICAL CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

nvd v2.0 7.5 HIGH AV:N/AC:L/Au:N/C:P/I:P/A:P

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