Executive brief
WSO2 API Manager's Webhook feature uses weak random number generation to create HMAC secrets that authenticate event payloads between systems. An attacker with sufficient computational resources could predict these secrets and forge valid webhook messages, allowing unauthorized injection or manipulation of events that downstream systems would trust as legitimate.
Technical details
The API Publisher component in WSO2 API Manager uses a non-cryptographic pseudorandom number generator (PRNG) to create shared secrets for Webhook HMAC validation, introducing insufficient entropy for security-sensitive operations. The root cause is the use of weak randomness in the secret generation mechanism, making the secrets predictable to a sophisticated attacker with adequate computational resources. Attack vector is network-based and requires no authentication or user interaction; an attacker must perform computational analysis to predict secrets. Successful exploitation enables forging event payloads with valid HMAC signatures, bypassing authenticity checks and potentially leading to unauthorized event injection and downstream system compromise. Patches are available via WSO2 Updates for affected versions (4.1.0 through 4.5.0), with a public GitHub fix at https://github.com/wso2/apim-apps/pull/1279.
Affected products
- WSO2 API Control Plane 4.5.0
- WSO2 API Manager 4.1.0, 4.2.0, 4.3.0, 4.4.0, 4.5.0
Timeline
- 2026-07-04: disclosed
- 2026-07-04: patched: Updates available for support subscription holders; public fix on GitHub