Coraza JSON key collision parser differential bypass

Severity: medium · CVSS 5.8 · Published 2026-10-08

Coraza is a Web Application Firewall (WAF) that inspects HTTP requests to block attacks like SQL injection and cross-site scripting. A flaw in how Coraza processes JSON payloads allows attackers to hide malicious nested properties by adding a decoy top-level property with a dotted name. The WAF examines only the harmless decoy while backend applications still see and process the malicious nested value, defeating attack detection rules from OWASP Core Rule Set.

Technologies: Coraza, github.com/corazawaf/coraza/v3 (Go). Vendors: Coraza, Go.

Quick answers

Is This vulnerability exploited in the wild?
No. Junglewise Threat Intelligence has no report of This vulnerability being exploited in the wild.
How severe is This vulnerability?
Medium severity, with a CVSS score of 5.8, published 8 October 2026.
Which products and versions are affected?
Coraza 3.8.0 and earlier; github.com/corazawaf/coraza/v3 (Go) >= 3.0.0, < 3.8.1.
Is there a fix for This vulnerability?
Yes: fixed in 3.8.1. Until then: Disable JSON body processing if not required for the application. Alternatively, restrict JSON requests to those with known safe structure and validate all nested object properties at the application layer before processing. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
How is This vulnerability attacked?
It is attacked over the network, in a software library.
Am I affected?
Check whether you run Coraza or github.com/corazawaf/coraza/v3 (Go) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

How to fix

  • Fixed in: 3.8.1

Disable JSON body processing if not required for the application. Alternatively, restrict JSON requests to those with known safe structure and validate all nested object properties at the application layer before processing.

Technical details

Coraza's JSON body processor flattens nested JSON properties into dot-separated variable names without escaping literal dots in property names. Two distinct JSON properties—a nested path like `account.role` and a literal top-level key `"account.role"`—both flatten to the same Coraza variable key, causing the later value to overwrite the earlier one in the processor's internal map. A case-folding variant affects keys differing only in case (e.g., `role` vs `Role`). Standard JSON parsers preserve both properties as distinct, creating a parser differential that allows inspection bypass.

Affected products

  • Coraza Coraza 3.8.0 and earlier

Timeline

  • 2026-10-08: disclosed

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