# CVE-2026-27193: Feathers exposes internal headers via unencrypted session cookie

> Attackers can decode session cookies to expose internal headers, API keys, and infrastructure details when deployed behind proxies.

- **Severity:** High 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`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 21 Feb 2026
- **Updated:** 25 Feb 2026
- **Also known as:** GHSA-9m9c-vpv5-9g85

## What is CVE-2026-27193?

CVE-2026-27193 is a high-severity vulnerability in feathersjs feathers, published on 21 Feb 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Feathersjs is a framework for creating web APIs and real-time applications with TypeScript or JavaScript. In versions 5.0.39 and below, 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, then 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. This issue has been fixed in version 5.0.40.

Weakness: CWE-200 (Exposure of Sensitive Information to an Unauthorized Actor)

## Which versions are affected by CVE-2026-27193?

2 open source packages ship an affected version, including @feathersjs/authentication-oauth. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `@feathersjs/authentication-oauth` | npm | All versions | 5.0.40 |
| `@feathersjs/authentication-oauth` | npm | All versions | 5.0.40 |

Products: Feathersjs Feathers.

## How do I fix CVE-2026-27193?

Upgrade @feathersjs/authentication-oauth to 5.0.40 or later.

## Is CVE-2026-27193 being exploited?

There is no known exploitation of CVE-2026-27193 in the wild and no public exploit code.

## Other vulnerabilities in feathersjs feathers

- [CVE-2026-29792](https://insights.sbomify.com/CVE-2026-29792/): Feathersjs has an OAuth Callback Account Takeover (critical 9.3)
- [CVE-2026-29793](https://insights.sbomify.com/CVE-2026-29793/): NoSQL Injection via WebSocket id Parameter in MongoDB Adapter (critical 9.3)
- [CVE-2026-27192](https://insights.sbomify.com/CVE-2026-27192/): Feathers has an origin validation bypass via prefix matching (high 7.6)
- [CVE-2023-37899](https://insights.sbomify.com/CVE-2023-37899/): feathersjs socket handler allows abusing implicit toString (high 7.5)
- [CVE-2026-27191](https://insights.sbomify.com/CVE-2026-27191/): Feathers: Open Redirect in OAuth callback enables account takeover (high 7.4)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-27193 and fix it if it is affected.

What it is: CVE-2026-27193 is a high-severity vulnerability in feathersjs feathers, published on 21 Feb 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-27193 in the wild and no public exploit code.

Affected packages and fixed versions:
- @feathersjs/authentication-oauth (npm): affected all versions; fixed in 5.0.40
- @feathersjs/authentication-oauth (npm): affected all versions; fixed in 5.0.40

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-27193/ (Markdown: https://insights.sbomify.com/CVE-2026-27193/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-27193
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-27193
- OSV: https://osv.dev/vulnerability/CVE-2026-27193

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-27193/
Summaries are generated and may contain mistakes; the official description above is the record.