Parse Server has a login timing side-channel reveals user existence

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

6.3 · CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N · score source

EPSS

• CVE-2026-39321: 0.23% estimated exploitation activity in the next 30 days; percentile 13.90 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

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.

Published by the source

8 Apr 2026, 00:07 UTC

Last modified by the source

15 Apr 2026, 21:34 UTC

Source last checked

26 Oct 2026, 12:48 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-mmpq-5hcv-hf2v

2. Revision 2 · amended · 25 Oct 2026

   Reviewed OSV alias/range/CVSS4 correction; package source scopes and original publication preserved. No customer finding resolved.

3. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-mmpq-5hcv-hf2v

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# Patch Next advisory brief: CVE-2026-39321

Advisory: Parse Server has a login timing side-channel reveals user existence
IDs: CVE-2026-39321, GHSA-mmpq-5hcv-hf2v
Record: https://patchnext.com/advisories/cve-2026-39321 (revision 3, source checked 26 Oct 2026, 12:48 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: parse-server 9.8.0-alpha.6, 8.6.74. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm parse-server: affected >= 9.0.0, < 9.8.0-alpha.6; < 8.6.74; fixed in 8.6.74, 9.8.0-alpha.6

## Suggested inspection (read-only)
- `npm ls parse-server --all`: lists every installed copy and version, including transitive ones. Run in the project root after `npm ci`.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on parse-server.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-mmpq-5hcv-hf2v (OSV record GHSA-mmpq-5hcv-hf2v lists affected ranges: npm parse-server >=9.0.0 =0 <8.6.74 (fixed))
- Verified: https://github.com/advisories/GHSA-mmpq-5hcv-hf2v (GitHub-reviewed advisory GHSA-mmpq-5hcv-hf2v lists affected ranges: npm parse-server >=9.0.0 =0 <8.6.74)

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