criticalAuthentication
5 min read2026-06-09
JWT alg confusion: forging tokens by switching RS256 to HS256
AN
anon
security researcher · vault ocean
The public key, served at a well-known endpoint, was accepted as an HMAC secret when the alg header was changed.
The verifier trusted the token's own alg header. Switching RS256→HS256 and signing with the public key produced a token the server accepted. Fix: pin the expected algorithm server-side; never let the token choose.
You read it — record it
sign in to record this and keep your streak alive
Reading earns +25ƒ and keeps your streak alive.
AN
Written by
anon
Security researcher · Vault Ocean contributor