Sync-in Server has Username Enumeration via Timing Attack

Exploitation

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

CVSS 4.0

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

EPSS

• CVE-2026-41161: 0.33% estimated exploitation activity in the next 30 days; percentile 26.57 (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.

Summary The /api/auth/login endpoint contains a logic flaw that allows unauthenticated remote attackers to enumerate valid usernames by measuring the application's response time. Details The logic flaw can be located at the below point in source: https://github.com/Sync-in/server/blob/7868bb2b3025f92e6c38087456304758713971b2/backend/src/applications/users/services/users-queries.service.ts#L91-L95 Endpoints used for authentication should respond to the user with a consistent cadence, preventing remote actors from deriving sensitive information about an application based on backend behavior. In the case of authentication endpoints, this timing discrepancy is often caused by short-circuiting due to the lack of a matched user to compare against - as is the case with Sync-in. Validation TickTock Enum (Burp Suite Extension) was utilized to validate this finding. Authentication attempts with a valid username see a response from the application at around 350-400ms on average, while invalid…

Published by the source

15 Apr 2026, 18:57 UTC

Last modified by the source

12 May 2026, 17:16 UTC

Source last checked

26 Oct 2026, 12:51 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-43fj-qp3h-hrh5

2. Revision 2 · amended · 24 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-43fj-qp3h-hrh5

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# Patch Next advisory brief: CVE-2026-41161

Advisory: Sync-in Server has Username Enumeration via Timing Attack
IDs: CVE-2026-41161, GHSA-43fj-qp3h-hrh5
Record: https://patchnext.com/advisories/cve-2026-41161 (revision 3, source checked 26 Oct 2026, 12:51 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 6.9)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: @sync-in/server 2.2.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm @sync-in/server: affected <= 2.1.0; fixed in 2.2.0

## Suggested inspection (read-only)
- `npm ls @sync-in/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 @sync-in/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-43fj-qp3h-hrh5 (OSV record GHSA-43fj-qp3h-hrh5 lists affected ranges: npm @sync-in/server >=0 <2.2.0 (fixed))
- Verified: https://github.com/advisories/GHSA-43fj-qp3h-hrh5 (GitHub-reviewed advisory GHSA-43fj-qp3h-hrh5 lists affected ranges: npm @sync-in/server >=0 <=2.1.0)

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