Fix bcrypt timing - #4007
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…id-vs-invalid-usernames / uaa ai-assisted=yes Co-authored-by: Cursor <cursoragent@cursor.com>
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Pull request overview
This PR mitigates a timing side-channel in UAA password authentication by making the “user not found” path perform a dummy BCrypt verification, reducing the ability to distinguish valid vs invalid usernames based on response latency.
Changes:
- Added a fixed dummy BCrypt hash constant for timing equalization.
- When a user lookup returns null, perform
PasswordEncoder#matchesagainst the dummy hash (for non-empty credentials) before returningBadCredentials.
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| private static final String DUMMY_BCRYPT_HASH = "{bcrypt}$2a$10$xn3igMIdgceZX.mK6/0.n.MvJk1.L/0R15Tz3gGZ/7eM/T.xI.1wO"; | ||
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| if (user == null) { | ||
| if (((CharSequence) req.getCredentials()).length() != 0) { | ||
| encoder.matches((CharSequence) req.getCredentials(), DUMMY_BCRYPT_HASH); | ||
| } |
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Ticket: bcrypt-timing-oracle-distinguishes-valid-vs-invalid-usernames
Fix: Added a dummy BCrypt hash validation step when the user is not found during authentication, balancing response latency to prevent username enumeration via timing attacks.