CVE-2026-54735: prebid-server's request forgery vulnerability allows for possible host environment data extraction

Should you act?

Critical and remotely reachable

No known exploitation yet, but it is network-reachable without credentials. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• No confirmed exploitation. It is not in CISA’s KEV catalog and CISA’s SSVC assessment records no known exploitation. That can change quickly after a public write-up; re-check if you are affected.
• EPSS 0.6%, percentile 49: FIRST’s model estimates a 0.6% chance of exploitation activity in the next 30 days, higher than 49% of all scored CVEs (low). EPSS is a probability, not a verdict.
• Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
• Only applies if your dependency tree includes github.com/prebid/prebid-server/v4 (Go) < 4.4.0, fixed in 4.4.0; github.com/prebid/prebid-server/v3 (Go) <= 3.30.0, no fixed version listed; github.com/prebid/prebid-server/v2 (Go) <= 2.32.0, no fixed version listed; github.com/prebid/prebid-server (Go) <= 0.275.0, no fixed version listed. Check your lockfile, including transitive dependencies.

What it is

Prebid Server is an open-source solution for running real-time advertising auctions in the cloud. Prior to version 4.4.0, certain bidder adapters in Prebid Server interpolate user-supplied parameters into outbound request URLs without properly validating host and subdomain values, allowing crafted bid request parameters to cause server-side requests to unintended destinations and potentially expose internal network services or sensitive server endpoints. This issue is fixed in version 4.4.0.

From the GitHub advisory

Impact Certain bidder adapters accept user-supplied parameters that are interpolated into outbound request URLs. Without proper input validation, a malicious actor could craft bid request parameters that cause the server to send HTTP requests to unintended destinations, potentially exposing internal network services or sensitive server endpoints to unauthorized access.

Patches Patched in v4.4.0

Workarounds If one is unable to update, please make sure that the affected bidder adapters are disabled.

Weakness type: CWE-918.

Product: github.com/prebid/prebid-server/v4 (Go) · Assigned by: GitHub_M · Published: 2026-07-29

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: low
• Privileges required: none (no login)
• User interaction: none
• Scope: changed (can affect other components)

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

• CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
• CISA SSVC assessment: exploitation none, automatable yes, technical impact total.
• FIRST EPSS (model of 2026-10-21): 0.61% probability of exploitation activity in the next 30 days; percentile 49.

Timeline

• 2026-07-29 — CVE record last updated
• 2026-07-29 — CVE record published by GitHub_M
• 2026-07-29 — GitHub-reviewed advisory GHSA-4p3g-4hcj-wpvx published (critical)

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vulnerability records

1. GitHub Advisory GHSA-4p3g-4hcj-wpvx github.com
2. CVE.org record CVE-2026-54735 cve.org
3. NVD entry CVE-2026-54735 nvd.nist.gov

Other references from the CVE record and advisory

1. github.com github.com
2. github.com github.com
3. github.com github.com
4. github.com github.com

Critical Go advisories · Today’s Security Digest