CVE-2024-23647 is a medium-severity (CVSS 6.5) Improper Authentication vulnerability in goauthentik.io. A fix is available for goauthentik.io — see the affected versions and patch details below.
PKCE downgrade attack in Authentik
Exploitation Status
No confirmed exploitation observed yet
- A successful exploit gives an attacker total control of the affected component, not partial access.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2024-23647.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
Where this sits among everything scored
Real-World Exposure
goauthentik.io🐹goauthentik.ioReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.
Description
Summary
PKCE is a very important countermeasure in OAuth2 , both for public and confidential clients. It protects against CSRF attacks and code injection attacks. Because of this bug, an attacker can circumvent the protection PKCE offers.
Patches
authentik 2023.8.7 and 2023.10.7 fix this issue.
Details
There is a bug in our implementation of PKCE that allows an attacker to circumvent the protection that PKCE offers. PKCE adds the code_challenge’ parameter to the authorization request and adds the code_verifier’ parameter to the token request. We recently fixed a downgrade attack (in v2023.8.5 and 2023.10.4) where if the attacker removed the code_verifier’ parameter in the token request, authentik would allow the request to pass, thus circumventing PKCE’s protection. However, in the latest version of the software, another downgrade scenario is still possible: if the attacker removes the code_challenge’ parameter from the authorization request, authentik will also not do the PKCE check.
Note that this type of downgrade enables an attacker to perform a code injection attack, even if the OAuth client is using PKCE (which is supposed to protect against code injection attacks). To start the attack, the attacker must initiate the authorization process without that code_challenge’ parameter in the authorization request. But this is easy to do (just use a phishing site or email to trick the user into clicking on a link that the attacker controls – the authorization link without that code_challenge’ parameter).
The OAuth BCP (https://datatracker.ietf.org/doc/html/draft-ietf-oauth-security-topics) explicitly mentions this particular attack in section 2.1.1: “Authorization servers MUST mitigate PKCE Downgrade Attacks by ensuring that a token request containing a code_verifier parameter is accepted only if a code_challenge parameter was present in the authorization request, see Section 4.8.2 for details.”
For more information
If you have any questions or comments about this advisory:
- Email us at [email protected]
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹Go | goauthentik.io | ≥ 2023.10.0&&< 2023.10.7 | 2023.10.7go get goauthentik.io@v2023.10.7 |
| 🐹Go | goauthentik.io | all versions | 2023.8.7go get goauthentik.io@v2023.8.7 |
Affected Products
authentikgoauthentikDetection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for goauthentik.io, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update goauthentik.io to 2023.10.7 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2024-23647 is resolved across your whole dependency graph.
Workarounds
Stop passing untrusted input into the interpreter or shell: call the affected binary with an argument array rather than a composed command string, reject anything outside a strict allowlist of expected values, and run the component under an account that cannot reach beyond the work it legitimately does.
Frequently Asked Questions
Is CVE-2024-23647 in your dependencies?
Find it across Go, including transitive dependencies.