How severe is CVE-2020-15222?

CVE-2020-15222 has a CVSS score of 8.1/10, rated HIGH. Immediate patching is strongly recommended.

Which packages are affected by CVE-2020-15222?

CVE-2020-15222 affects the following packages: github.com/ory/fosite (Go). Ecosystems affected: Go.

How do I fix CVE-2020-15222?

Update github.com/ory/fosite to 0.31.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2020-15222 is resolved across your whole dependency graph.

How do I detect CVE-2020-15222 in my Go dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/ory/fosite, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2020-15222 if there is no patch (or I can't update yet)?

Put an independent control in front of the weakness: restrict the affected endpoint or interface to trusted networks, require an additional authentication factor or proxy-level check, and invalidate existing sessions and credentials in case the flaw has already been used.

Is CVE-2020-15222 actively exploited in the wild?

Yes. There are 1 known exploit references for CVE-2020-15222, including 1 in-the-wild exploitation observed on GitHub and other sources. Treat this as actively exploitable and prioritize patching immediately. All exploit code should only be run in an isolated sandbox environment for research or authorized testing — never against production systems without explicit written authorization.

What is the EPSS score for CVE-2020-15222?

CVE-2020-15222 has an EPSS (Exploit Prediction Scoring System) score of 0.9%, placing it in the 57th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2020-15222?

CVE-2020-15222 is classified as Improper Authentication (CWE-287), CWE-345 (CWE-345). These weakness types describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2020-15222 published, and has it been updated?

CVE-2020-15222 was published on September 24, 2020 and was last updated on July 9, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐹

🐹 Go

Not in CISA KEV

HIGH severity

CVE-2020-15222 — fosite

HIGHFix: ory/fosite@0c9e0f6

CVE-2020-15222 is a high-severity (CVSS 8.1) Improper Authentication vulnerability in github.com/ory/fosite. 1 public exploit reference exists, so weaponization risk is real. A fix is available for github.com/ory/fosite — see the affected versions and patch details below.

Token reuse in Ory fosite

Also known asGHSA-v3q9-2p3m-7g43GO-2021-0110

Published

Sep 24, 2020

Updated

Jul 9, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

1 known

Exploitation data as of Oct 9, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗

0.9%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs57th percentile — riskier than 57% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

CVE-2020-15222 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 385,738 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.

Real-World Exposure

1 pkg affected

🐹github.com/ory/fosite

Real-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

Impact

When using client authentication method "private_key_jwt" [1], OpenId specification says the following about assertion jti:

A unique identifier for the token, which can be used to prevent reuse of the token. These tokens MUST only be used once, unless conditions for reuse were negotiated between the parties

Hydra does not seem to check the uniqueness of this jti value. Here is me sending the same token request twice, hence with the same jti assertion, and getting two access tokens:

$ curl --insecure --location --request POST 'https://localhost/_/oauth2/token' \
   --header 'Content-Type: application/x-www-form-urlencoded' \
   --data-urlencode 'grant_type=client_credentials' \
   --data-urlencode 'client_id=c001d00d-5ecc-beef-ca4e-b00b1e54a111' \
   --data-urlencode 'scope=application openid' \
   --data-urlencode 'client_assertion_type=urn:ietf:params:oauth:client-assertion-type:jwt-bearer' \
   --data-urlencode 'client_assertion=eyJhb [...] jTw'
{"access_token":"zeG0NoqOtlACl8q5J6A-TIsNegQRRUzqLZaYrQtoBZQ.VR6iUcJQYp3u_j7pwvL7YtPqGhtyQe5OhnBE2KCp5pM","expires_in":3599,"scope":"application openid","token_type":"bearer"}⏎
$ curl --insecure --location --request POST 'https://localhost/_/oauth2/token' \
   --header 'Content-Type: application/x-www-form-urlencoded' \
   --data-urlencode 'grant_type=client_credentials' \
   --data-urlencode 'client_id=c001d00d-5ecc-beef-ca4e-b00b1e54a111' \
   --data-urlencode 'scope=application openid' \
   --data-urlencode 'client_assertion_type=urn:ietf:params:oauth:client-assertion-type:jwt-bearer' \
   --data-urlencode 'client_assertion=eyJhb [...] jTw'
{"access_token":"wOYtgCLxLXlELORrwZlmeiqqMQ4kRzV-STU2_Sollas.mwlQGCZWXN7G2IoegUe1P0Vw5iGoKrkOzOaplhMSjm4","expires_in":3599,"scope":"application openid","token_type":"bearer"}

Patches

This issue is patched in 0.31.0.

Workarounds

Do not allow clients to use private_key_jwt.

References

https://openid.net/specs/openid-connect-core-1_0.html#ClientAuthentication

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐹Go	`github.com/ory/fosite`	all versions	0.31.0`go get github.com/ory/fosite@v0.31.0`

Affected Products

1 product · 1 configurations

Application

fositeory

< 0.31.0

range

Exploits & PoCs

Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.

In ORY Fosite (the security first OAuth2 & OpenID Connect framework for …

github.comNVDOct 2020

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/ory/fosite, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update github.com/ory/fosite to 0.31.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2020-15222 is resolved across your whole dependency graph.
Workarounds
Put an independent control in front of the weakness: restrict the affected endpoint or interface to trusted networks, require an additional authentication factor or proxy-level check, and invalidate existing sessions and credentials in case the flaw has already been used.

Frequently Asked Questions

### Impact When using client authentication method "private_key_jwt" [[1]](https://openid.net/specs/openid-connect-core-1_0.html#ClientAuthentication), OpenId specification says the following about assertion `jti`: > A unique identifier for the token, which can be used to prevent reuse of the token. These tokens MUST only be used once, unless conditions for reuse were negotiated between the parties Hydra does not seem to check the uniqueness of this `jti` value. Here is me sending the same token request twice, hence with the same `jti` assertion, and getting two access tokens: ``` $ curl -