Critical Prebid Server SSRF Flaw (CVE-2026-54735) Lets Attackers Reach Cloud Metadata Endpoints

What's the vulnerability?

CVE-2026-54735 is a server-side request forgery (SSRF) vulnerability in prebid/prebid-server, classified under CWE-918 and rated CVSS 10.0. The root cause is insufficient validation of URL and adapter parameters embedded in bid requests: an attacker can craft a bid request or adapter configuration that forces the prebid-server host to issue an outbound HTTP request to a destination of the attacker's choosing.

Because prebid-server frequently runs in cloud-hosted ad-tech infrastructure, the practical impact is severe — a crafted request can redirect the server's outbound call to internal services or to the cloud instance metadata endpoint (169.254.169.254), potentially exfiltrating IAM credentials, instance metadata, or responses from internal services that were never meant to be internet-reachable.

Affected software

• Vendor/ecosystem: go
• Products: github.com/prebid/prebid-server/v4, github.com/prebid/prebid-server/v3, github.com/prebid/prebid-server/v2, github.com/prebid/prebid-server
• Affected versions: < 4.4.0, <= 3.30.0, <= 2.32.0, and <= 0.275.0

No patched date is currently recorded in our tracking, so treat all listed version lines as vulnerable until you've confirmed a fix with the vendor.

Exploitation status

This vulnerability was disclosed on 2026-07-29 and currently has a public proof-of-concept available. There is no indication yet that it's been added to CISA's KEV catalog or observed in active mass exploitation, but a public PoC combined with a CVSS 10.0 score and straightforward request-crafting means the barrier to weaponization is low. Defenders running prebid-server, particularly in cloud environments, should treat this as an urgent priority for detection and mitigation.

How our detection catches it

Our rule focuses on the network behavior that SSRF exploitation produces rather than the request payload alone, since bid/adapter parameters can be obfuscated or vary widely. Specifically, it looks for anomalous outbound HTTP requests originating from prebid-server processes or containers that are directed at:

• Internal RFC1918 address ranges
• Loopback addresses
• Link-local cloud metadata IPs, notably 169.254.169.254
• Unexpected external hosts triggered during bid or adapter request handling

By correlating these outbound connection patterns with the prebid-server process/container identity, the rule can flag SSRF attempts even when the underlying bid request payload itself doesn't trip a simple signature match. This logic ships across our full SIEM coverage: Microsoft Sentinel (KQL), Splunk (SPL), Elastic (EQL), IBM QRadar (AQL), Sumo Logic, Google Chronicle (YARA-L), and CrowdStrike (CQL), so teams can deploy it in whichever stack they run.

Learn more

For the full detection logic, MITRE ATT&CK mapping, and ready-to-deploy queries across all supported SIEMs, see the CVE-2026-54735 detection page.