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Fencer Vulns
medium 6.1

CVE-2020-15233 json

OAuth2 Redirect URL validity does not respect query parameters and character casing for loopback addresses

published 2020-10-02 6 y ago modified 2026-07-08 4 mo ago also GHSA-rfq3-w54c-f9q5 , EUVD-2021-1179

cvss
6.1
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.8%
EPSS 0.8% chance of exploitation in 30 days, percentile 56%
public exploits
0
none known

Summary

ORY Fosite is a security first OAuth2 & OpenID Connect framework for Go. In Fosite from version 0.30.2 and before version 0.34.1, there is an issue in which an an attacker can override the registered redirect URL by performing an OAuth flow and requesting a redirect URL that is to the loopback adapter. Attackers can provide both custom URL query parameters to their loopback redirect URL, as well as actually overriding the host of the registered redirect URL. These attacks are only applicable in scenarios where the attacker has access over the loopback interface. This vulnerability has been patched in ORY Fosite v0.34.1.

Patch / fix

  • go github.com/ory/fosite 0.34.1
  • ory fosite 0.34.1

Exploit prediction

0.80% chance of exploitation in the next 30 days, higher than 56% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 6.1 CVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:U/C:H/I:H/A:N
NVD 3.1 4.8 CVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:C/C:L/I:L/A:N
NVD 2.0 4.9 AV:N/AC:M/Au:S/C:P/I:P/A:N
GitHub 3.0 6.1 CVSS:3.0/AV:N/AC:L/PR:H/UI:R/S:U/C:H/I:H/A:N/E:P/RL:O/RC:C

Affected packages

ecosystem package affected fixed in
go github.com/ory/fosite
>=0.30.3, <0.34.1
0.34.1

Affected products

  • ory fosite

Classification

Weakness
  • CWE-20 Improper Input Validation
  • CWE-601 URL Redirection to Untrusted Site

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.