Prototype Pollution CVE-2026-48795

Summary

The fix for GHSA-f5x2-vj4h-vg4c / CVE-2026-25754 introduced in commit 40e1c71 is incomplete and can be bypassed through nested prototype pollution payloads.

The original patch replaced the internal FormFields storage object with Object.create(null), preventing direct payloads such as __proto__.polluted. However, payloads containing a non-dangerous segment before __proto__ or constructor.prototype, such as user.__proto__.polluted, still lead to Object.prototype pollution.

This issue is exploitable remotely through a single unauthenticated multipart/form-data request using the default configuration.

Affected versions

• >= 10.1.3 < 10.1.5
• >= 11.0.0-next.9 < 11.0.3

Details

The regression tests added by the original fix only covered direct payloads such as:

• __proto__.polluted
• constructor.prototype.polluted

These payloads are blocked because the root object no longer inherits from Object.prototype.

However, lodash _.set() (via @poppinss/utils) still creates intermediate objects using plain {} values. Once a normal segment is encountered, subsequent __proto__ or constructor.prototype segments regain access to Object.prototype.

Impact

An unauthenticated attacker can remotely pollute Object.prototype on any route accepting multipart/form-data requests behind BodyParserMiddleware.

Because the pollution is process-wide, the impact may include authorization bypasses, unexpected behavior in downstream libraries, or prototype pollution gadget chains leading to remote code execution.

Patches

Fixes targeting v6 and v7 have been published below.

Users should upgrade to a version that includes the following fix:

• https://github.com/adonisjs/bodyparser/releases/tag/v10.1.5
• https://github.com/adonisjs/bodyparser/releases/tag/v11.0.3

References

• CWE-1321
• Prior advisory this bypasses: GHSA-f5x2-vj4h-vg4c / CVE-2026-25754