GHSA-w9mr-28mw-j8hg Hop-by-hop abuse to malform header mutator

Not scored Published 26 Apr 2023

Attackers can bypass header-based authentication or authorization by dropping headers via Connection header manipulation in Go-based gateways.

Exploited in the wild: Not known
Login needed: Not needed
Attackable: Over the internet
Victim action needed: Not needed
Fix: Available

What is GHSA-w9mr-28mw-j8hg?

GHSA-w9mr-28mw-j8hg is a vulnerability in github.com/ory/oathkeeper, published on 26 Apr 2023. An attacker can exploit it over the internet without logging in, with no action from the victim.

Official description

Impact

Downstream services relying on the presence of headers set by the header mutator could be exploited. A client can drop the header set by the header mutator by including that header's name in the Connection header. Example minimal config:

- id: &#39;example&#39;
  upstream:
    url: &#39;https://example.com&#39;
  match:
    url: &#39;http://127.0.0.1:4455/&#39;
    methods:
      - GET
  authenticators:
    - handler: anonymous
  authorizer:
    handler: allow
  mutators:
    - handler: header
      config:
        headers:
          X-Subject: {{ .Subject }}

curl -H &#34;Connection: close,x-subject&#34; http://127.0.0.1:4455/

The X-Subject header will not arrive at the downstream server. It is completely dropped. In case the downstream server handles such a request in an unexpected way, an attacker can exploit this, assuming they know or guess the internal header name.

Patches

c5cc7f736dc84185034be4356057d1c7a656d797

Workarounds

The downstream server should handle the case that an expected header is not set by responding with an appropriate error.

References

See background info in https://github.com/golang/go/issues/50580

Which versions are affected by GHSA-w9mr-28mw-j8hg?

3 open source packages ship an affected version, including github.com/ory/oathkeeper.

Package	Affected	Fixed in
`github.com/ory/oathkeeper` Go	All versions	`0.40.3`
`github.com/ory/oathkeeper` Go	All versions	`0.40.3`
`github.com/ory/oathkeeper` Go	All versions	`0.40.3`

How do I fix GHSA-w9mr-28mw-j8hg?

Upgrade github.com/ory/oathkeeper to 0.40.3 or later.

Is GHSA-w9mr-28mw-j8hg being exploited?

There is no known exploitation of GHSA-w9mr-28mw-j8hg in the wild and no public exploit code.

Sources

Also known as GO-2023-1747.