CVE-2026-113603

What it is

The x402 SIWX server extension in @x402/extensions 2.3.1 through 2.28.0, x402 PyPI 2.11.0 through 2.25.0, and Go module 2.16.0 through 2.28.0 contains an authorization bypass vulnerability that allows paying clients to unlock unpaid routes by supplying a mismatched PaymentPayload.resource URL. Attackers can pay for the cheapest SIWX-protected route while setting resource.url to an expensive route, then repeatedly access it using only a SIGN-IN-WITH-X header without further payment.

At a glance

Exploitability

Can be exploited over the network without logging in. Limited direct impact.

Exploit odds

0.4% chance of exploitation in the next 30 days (EPSS).

Fix

A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

1. 2026-10-20 11:48 UTC ReservedThe CVE id was reserved by its CNA
2. 2026-10-20 16:17 UTC PublishedDisclosed publicly on CVE.org and NVD
3. 2026-10-21 16:17 UTC Last updatedMost recent change to the record

Why it ranks here

• Exploited in the wild: no, CISA does not list it.
• Exploit odds: 0.4% in the next 30 days (EPSS).
• Severity: 6.9 MEDIUM (CVSS).
• Fix: a patch or advisory is linked.

Details

Published

2026-10-20 16:17 UTC

Last modified

2026-10-21 16:17 UTC

Exploit probability

0.4% · EPSS, next 30 days

Weakness

CWE-639 · Insecure direct object reference

Record status

Awaiting Analysis

Attack profile CVSS 4.0 · 6.9

Attack vector

Network

Complexity

Low

Attack requirements

None

Privileges needed

None

User interaction

None

Confidentiality

Low

Integrity

Low

Availability

None

Is it in your code?

Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.

Read https://cve-list.com/agent/cve/CVE-2026-113603.md and follow it. Check whether this project is affected by CVE-2026-113603. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.

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