Parse Server has a login timing side-channel reveals user existence
Impact
The login endpoint response time differs measurably depending on whether the submitted username or email exists in the database. When a user is not found, the server responds immediately. When a user exists but the password is wrong, a bcrypt comparison runs first, adding significant latency. This timing difference allows an unauthenticated attacker to enumerate valid usernames.
Patches
A dummy bcrypt comparison is now performed when no user is found, normalizing response timing regardless of user existence. Additionally, accounts without a stored password (e.g. OAuth-only) now also run a dummy comparison to prevent the same timing oracle.
Workarounds
Configure rate limiting on the login endpoint to slow automated enumeration. This reduces throughput but does not eliminate the timing signal for individual requests.
Affected software
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| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| npm package | parse-server | >= 9.0.0, < 9.8.0-alpha.6, < 8.6.74 | 9.8.0-alpha.6, 8.6.74 |
References
- https://github.com/parse-community/parse-server/security/advisories/GHSA-mmpq-5hcv-hf2v
- https://nvd.nist.gov/vuln/detail/CVE-2026-39321
- https://github.com/parse-community/parse-server/pull/10398
- https://github.com/parse-community/parse-server/pull/10399
- https://github.com/parse-community/parse-server
- CVSS vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N- Weakness (CWE)
CWE-208- Platform
- npm
- Package
parse-server- Disclosed
- 08.04.2026
- Updated
- 11.10.2026 10:22
Sources and licenses
OSV / GitHub Advisory Database - GHSA-mmpq-5hcv-hf2v - CC BY 4.0
Vulnerability history: parse-server
All published vulnerabilities of this package (npm package), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 116
- First → latest
- 06.2019 06.2026
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- Critical 17
- High 49
- Medium 40
- Low 10
Disclosures per year
- 2019: 2
- 2020: 4
- 2021: 4
- 2022: 12
- 2023: 5
- 2024: 4
- 2025: 6
- 2026: 79
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Parse Server has a login timing side-channel reveals user existence this entry
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