Amazon Web Services Inc. has patched a flaw across seven of its software development kits after product security startup Pi Inc. traced a single bug report to roughly 2,500 instances of the same defect, Pi revealed today.

Every AWS SDK builds the hostname it calls from a template. The region drops into the middle of https://{service}.{region}.amazonaws.com. A valid region looks like us-east-1. On the vulnerable code paths, nothing checked for that.

Plenty of applications let a user pick the region, so Pi’s researchers picked “@attacker.com#”. The SDK built https://sts.@attacker.com#.amazonaws.com and signed a request to that address. A URL parser reads everything before the @ as a username. Everything after the # gets discarded. What survives is attacker.com.

Redirecting an ordinary application programming interface call leaks a request signature. That is survivable. The AssumeRoleWithWebIdentity call made by Elastic Kubernetes Service workloads, Cognito applications and OpenID Connect integrations is not ordinary. That request carries a bearer token in its body, in plaintext.

In one authorized engagement the target ran inside EKS. The redirected call carried the pod’s Kubernetes service account token to a server the testers controlled. Replaying it to AWS Security Token Service returned live credentials inside the customer’s account.

Pi said it handed its platform the original report and nothing else, with no per-language rules and no list of services to check. The software abstracted the vulnerable code into what the company calls an anti-pattern, a description of the behavior rather than the syntax, then went looking for that behavior elsewhere.

AWS generates SDK clients for more than 400 services from shared service models, so a missing check in the generator lands everywhere at once. Python and Ruby had guarded against it for years. Most of the others had not.

The fix runs to a few lines. Validate the region as a host label, letters, digits and hyphens only, before it reaches the hostname. That validation lives inside each generated SDK, not in one shared place. AWS ended up writing it seven times.

Pi reported it to AWS on Oct. 14, 2025. A first patch was committed within a week. The advisories did not go out until Jan. 8 and Jan. 9. Go v2 was last. Only the .NET SDK drew a CVE, CVE-2026-22611, rated low at 3.7 on the CVSS scale, and Pi co-founder and Chief Executive Guy Arazi is named in the acknowledgments.

AWS did not frame any of this as a vulnerability. Its advisories call the change a defense-in-depth enhancement. Validating that input, AWS says, is the developer’s job under the shared responsibility model.

Pi calls the rating incomplete. The company tested the flaw where it actually runs in third-party platforms that embed an AWS SDK and expose the region field and said seven of seven were exploitable. Each leaked live AWS credentials to a callback server.

Some were well-known companies and some were security vendors. All were notified and remediated before publication. A per-instance score rates one outcome in one place, Pi wrote, and has no way to express a class of behavior a code generator has copied into thousands of clients.

Pi  is based in San Francisco. Brightmind Partners and Third Point Ventures led a $35 million round for the company in June. CrowdStrike Holdings Inc. Chief Executive George Kurtz and Armis Inc. founders Yevgeny Dibrov and Nadir Izrael also also investors.

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