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Unlock with Pro - from £29/user/moDetect Prebid Server SSRF via Request Forgery (CVE-2026-54735) in Splunk
Detects exploitation of CVE-2026-54735, a critical (CVSS 10.0) server-side request forgery (SSRF) vulnerability in prebid/prebid-server affecting versions < 4.4.0, <= 3.30.0, <= 2.32.0, and <= 0.275.0. The flaw (CWE-918) allows an attacker to craft bid request or adapter/URL parameters that cause the prebid-server host to issue outbound requests to attacker-controlled or internal/cloud-metadata endpoints, potentially exfiltrating host environment data (cloud metadata credentials, internal service responses). Detection focuses on anomalous outbound HTTP requests originating from prebid-server processes/containers to internal RFC1918 ranges, loopback, link-local cloud metadata IPs (169.254.169.254), or unexpected external hosts triggered by bid/adapter request handling.
MITRE ATT&CK
SPL Detection Query
index=prebid_server sourcetype=prebid:access
| eval is_metadata=if(dest_ip="169.254.169.254",1,0)
| eval is_internal=if(match(dest_ip, "^(10\.|172\.(1[6-9]|2[0-9]|3[01])\.|192\.168\.|127\.)"),1,0)
| where (is_metadata=1 OR is_internal=1) AND (uri_path="/openrtb2/auction" OR uri_path="/openrtb2/amp" OR uri_path="/setuid" OR uri_path="/cookie_sync")
| stats count values(uri_path) as paths values(dest_ip) as destinations by src_ip, _time span=5m
| where count>1Detects Splunk-ingested prebid-server access logs showing outbound requests originating from auction/amp/setuid/cookie_sync handlers directed at metadata service or internal IP ranges, consistent with SSRF exploitation.
Data Sources
Required Sourcetypes
False Positives & Tuning
- Legitimate internal bidder adapter integrations
- Internal health-check probes
- Service mesh proxy hops through internal IP space
- Dev/test environments with mock internal adapter endpoints
Other platforms for CVE-2026-54735
Testing Methodology
Validate this detection against 4 adversary techniques from Atomic Red Team. Each test below lists the behaviour to exercise and the telemetry you should expect to see. Executable commands and cleanup steps are available with Pro.
- Test 1Simulate SSRF request to cloud metadata endpoint via crafted auction request
Expected signal: Outbound HTTP connection from prebid-server process to 169.254.169.254 logged in network flow/access logs with source path /openrtb2/auction
- Test 2Simulate SSRF probe to internal RFC1918 service via cookie_sync endpoint
Expected signal: Outbound HTTP connection from prebid-server process to internal IP 10.0.0.5 logged with request path /cookie_sync
- Test 3Version fingerprint check against vulnerable prebid-server release
Expected signal: HTTP GET request to /status or /version endpoint logged in prebid-server access logs
- Test 4Simulate repeated metadata-scanning pattern via openrtb2/amp endpoint
Expected signal: Multiple outbound HTTP connections from prebid-server process to distinct internal/metadata IPs within a short time window, logged with request path /openrtb2/amp
References (5)
- https://github.com/prebid/prebid-server/security/advisories/GHSA-4p3g-4hcj-wpvx
- https://github.com/prebid/prebid-server/pull/4802
- https://github.com/prebid/prebid-server/commit/494ac271cd4b5024df9123ef25ca3cff96390be3
- https://github.com/prebid/prebid-server/releases/tag/v4.4.0
- https://github.com/advisories/GHSA-4p3g-4hcj-wpvx
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