Feathers exposes internal headers via unencrypted session cookie

Exploitation

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

CVSS 4.0

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

EPSS

• CVE-2026-27193: 0.40% estimated exploitation activity in the next 30 days; percentile 34.09 (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.

All HTTP request headers are stored in the session cookie, which is signed but not encrypted, exposing internal proxy/gateway headers to clients. The OAuth service stores the complete headers object in the session: The session is persisted using cookie-session, which base64-encodes the data. While the cookie is signed to prevent tampering, the contents are readable by anyone by simply decoding the base64 value. Under specific deployment configurations (e.g., behind reverse proxies or API gateways), this can lead to exposure of sensitive internal infrastructure details such as API keys, service tokens, and internal IP addresses. Credits: Abdelwahed Madani Yousfi (@vvxhid) / Edoardo Geraci (@b0-n0-b0) / Thomas Rinsma (@ThomasRinsma) From Codean Labs.

Published by the source

19 Feb 2026, 20:32 UTC

Last modified by the source

23 Feb 2026, 23:43 UTC

Source last checked

26 Oct 2026, 12:42 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-9m9c-vpv5-9g85

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-9m9c-vpv5-9g85

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# Patch Next advisory brief: CVE-2026-27193

Advisory: Feathers exposes internal headers via unencrypted session cookie
IDs: CVE-2026-27193, GHSA-9m9c-vpv5-9g85
Record: https://patchnext.com/advisories/cve-2026-27193 (revision 3, source checked 26 Oct 2026, 12:42 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.2)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: @feathersjs/authentication-oauth 5.0.40. A vendor fix does not mean a deployment is fixed.

## Affected components
- npm @feathersjs/authentication-oauth: affected <= 5.0.39; fixed in 5.0.40

## Suggested inspection (read-only)
- `npm ls @feathersjs/authentication-oauth --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 @feathersjs/authentication-oauth.
- 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-9m9c-vpv5-9g85 (OSV record GHSA-9m9c-vpv5-9g85 lists affected ranges: npm @feathersjs/authentication-oauth >=0 <5.0.40 (fixed))
- Verified: https://github.com/advisories/GHSA-9m9c-vpv5-9g85 (GitHub-reviewed advisory GHSA-9m9c-vpv5-9g85 lists affected ranges: npm @feathersjs/authentication-oauth >=0 <=5.0.39)

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