How to Hunt for Forged Admin Tokens in API Gateway Logs

When an authentication bypassAuthentication Bypass📖A security vulnerability that allows an attacker to circumvent the login verification process and gain unauthorized access to a system without providing valid credentials. hits an API gatewayAPI Gateway🛡️A reverse proxy that sits in front of backend services, authenticating clients, enforcing rate limits and policy, and routing requests. Because it registers every client and stores every backend definition, an administrator on the gateway can reach credentials for everything it fronts., the intrusion does not look like an intrusion. There is no failed login, no brute-force spike, no malware dropped on a host. There is a request carrying a token that should have been rejected and was not, followed by ordinary-looking administrative activity. The WSO2 API Manager bypass CVE-2026-5430, added to CISA's Known Exploited Vulnerabilities catalog in September 2026, is exactly this kind of event: watchTowr observed attackers presenting pre-built JSON Web Tokens with administrator claims, and the only trace a victim would have is the request itself and what followed it. This guide is a practical process for finding those traces in gateway logs after the fact and for making sure they are there to find next time.

Start With the Question, Not the Log

Threat hunting fails when it starts by opening a log and scrolling. Start instead with the specific artifact the attack produces. For a forged-token bypass, there are three.

1. A request arriving with a bearer tokenBearer Token🛡️A credential presented in an HTTP Authorization header that grants access to whoever holds it, with no proof of identity beyond possession. Services must validate the token on every request; a code path that accepts any bearer value, as in CVE-2026-59822, is an authentication bypass. whose algorithm header is not one your deployment issues, or whose signature could not have been produced by your keys.
2. A session or API call executing with administrator scope for which there is no corresponding authentication event at the identity provider that issues your real tokens.
3. Administrative actions, such as exporting application credentials, listing backend endpoints, or creating new applications and keys, performed by that session.

Each of those maps to a different data source, and the hunt is a sequence: find candidate tokens, correlate to missing logins, then follow the session to see what it touched. Inception Security's published hunting notes for this CVE follow the same order and suggest starting the window on 13 September 2026, the date of the first honeypotHoneypot🛡️A decoy system deployed to be attacked so defenders can observe exploitation attempts safely. Honeypot networks give early warning that a vulnerability has moved from theoretical to actively exploited, often before official catalogs like CISA KEV confirm it. observation, extending backward only if your own data justifies it.

Step 1: Confirm What Your Logs Actually Capture

Before hunting, check that the evidence exists. Many gateway deployments log the request path, status code, and client IP but never the authorization header, because tokens are sensitive. That is a reasonable default and it is fatal to this hunt. You need at minimum the decoded token header (the algorithm and key ID fields), the subject and role claims, and a token fingerprint such as a hash, without necessarily storing the full token.

Sources to check, in rough order of value:

• **Gateway access and authentication logs.** In WSO2's case the gateway and the Carbon management console each produce HTTP access logs and authentication audit logs. Confirm which fields are enabled.
• **Reverse proxyReverse Proxy🛡️A server that sits in front of one or more backend services, terminating client connections and forwarding requests to the backend. It is the standard place to add authentication, TLS and access control to a service that lacks its own, without modifying the application. or WAF logs in front of the gateway.** If your edge terminates TLS and can log custom fields, it may have captured the authorization header even when the gateway did not.
• **Identity provider logs.** Every legitimate admin token corresponds to an issuance event. These logs are your ground truth for what "real" looks like.
• **Application and key audit history.** Changes to registered applications, consumer keys, and secrets are usually recorded in the gateway's own audit trail.
• **Host telemetry on gateway nodes.** Process and file activity on the node itself catches the case where an admin session was used to reach the underlying system.

If the authorization header was never logged, do not stop. Steps 2 and 3 work without it, they are just noisier.

Step 2: Find Tokens That Should Not Exist

With token headers available, the query is simple: list distinct algorithm values seen in bearer tokens over the window and compare against what your deployment issues. A correct deployment has exactly one or two values. Anything else is a candidate. Pay attention to the unsecured value, to HMAC family values appearing where you issue RSA-signed tokens, and to any value your verifier would not recognize, since the class of bug explained in How JWT Algorithm Confusion Lets a Forged Token Pass Signature Checks turns on the verifier mishandling exactly those.

Also check the key identifier field. A forged token either omits it or names a key you do not have. Both are anomalies.

Group the candidates by client IP, user agent, and the subject claim they asserted. Attackers scanning broadly, as the honeypot data suggests this actor was, tend to reuse a token across many targets, so the same subject and the same signature blob will show up on multiple nodes.

Step 3: Correlate Admin Sessions to Real Logins

This step works even without token logging. Pull every request that executed with administrator scope during the window, keyed by subject and approximate start time. For each, look for a matching issuance event at the identity provider within a plausible lead time. Sessions with no matching login are your primary finding.

Two refinements help. First, distinguish interactive logins from token refreshes and service-account issuance, so a long-lived automation identity does not drown out the signal. Second, look at the first request of each unexplained session. A forged-token attacker has no reason to visit a login page, so their session begins at an API call, typically an enumeration of applications, subscriptions, or backend definitions rather than a dashboard load.

Step 4: Follow the Session

For each unexplained admin session, reconstruct what it did. The high-value actions on an API gateway are enumerating registered applications and their consumer keys and secrets, reading backend endpoint definitions and any credentials stored with them, creating new applications or keys as a persistence mechanism, and modifying policies or mediation logic to redirect or copy traffic. Any of those turns a bypass into a durable compromise.

Cross-reference with the application audit history. A new key generated for an existing application, or a new application created by an admin identity that never logged in, is a strong indicator and a rotation trigger.

Step 5: Decide and Act

If step 2 or 3 produces confirmed findings, the response is not just patching. Treat every secret the gateway holds as exposed and rotate it, revoke and reissue application keys, and check backend services for authentication events using credentials that only the gateway should know. The playbook in How to Rotate Every Secret After a Server Compromise covers the sequencing. Report the incident internally with the token fingerprints and source addresses so the same actor can be blocked at the edge.

If the hunt comes up empty, record that outcome too, including which log sources you had and which you lacked. Under CISA's BOD 26-04BOD 26-04🛡️CISA Binding Operational Directive 26-04, issued 10 June 2026, which replaced BOD 22-01. It assigns federal civilian agencies remediation deadlines of 3, 14, or 60 days based on asset exposure, KEV status, exploit automation, and post-exploitation impact, and requires forensic triage for the 3-day tier. the forensic-triage requirement is explicit for federal agencies, and an auditor will ask what evidence a clean result rested on.

Making the Next Hunt Faster

The uncomfortable lesson from the WSO2 case is that a five-month-old patch was still unapplied when the attacks arrived, and most affected organizations will only now be checking whether they can even see a forged token. Three changes close that gap permanently.

• **Log token metadataMetadata📖Data about data—like email timestamps, file sizes, or location tags on photos., not tokens.** Emit the algorithm, key ID, subject, roles, expiry, and a hash of the signature on every authenticated request. That is enough to hunt with and safe enough to retain.
• **Alert on algorithm mismatch in real time.** A bearer token with an unexpected algorithm should page someone, not wait for a retrospective hunt.
• **Baseline admin-scope activity.** Know how many administrator sessions per day are normal, where they originate, and what their first request usually is. Deviations from that baseline are the earliest signal you will get when the next verifier bug ships.

None of that requires new tooling. It requires deciding that the gateway is a place where authentication is enforced and therefore a place where authentication must be observable, which is a policy choice more than a technical one.