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Fencer Intel
high 8.5

CVE-2026-56739 json

Logto: SSRF via Webhooks and Custom OAuth2 Connector UserInfo Endpoint

published 2mo ago modified last mo. also EUVD-2026-86224 , GHSA-3556-624q-c5w3

Unreviewed: the maintainers' own advisory

Published by the maintainers on their GitHub repository logto-io/logto. GitHub has not reviewed it into the GitHub Advisory Database, so the affected packages and versions are the maintainers' word. Read the full advisory on GitHub.

cvss
8.5
version 4.0, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.3%
EPSS 0.3% chance of exploitation in 30 days, percentile 22%
public exploits
0
none known

Summary

Logto is the modern, open-source auth infrastructure for SaaS and AI apps. Prior to 1.43.0, Logto fetches administrator-controlled outbound destinations without validating the address used for the connection. Webhook delivery in packages/core/src/libraries/hook/utils.ts can reach special-use and cloud metadata addresses. Custom OAuth2 connectors can use an attacker-selected userInfoEndpoint and forward the OAuth access token in the Authorization header, while OIDC connectors can fetch an attacker-selected jwksUri. The affected operations require tenant administrative configuration access, but they cross the server's network boundary and can expose internal data or upstream provider credentials. This issue is fixed in version 1.43.0.

Patch / fix

Is CVE-2026-56739 in your stack? Fencer shows which of your repositories are affected as soon as an advisory lands, and opens the fix as a pull request.

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CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
last mo.

Exploit prediction

0.30% chance of exploitation in the next 30 days, higher than 22% of all scored CVEs (FIRST EPSS, 2026-11-11).

CVSS scores

assigned by version score vector
CNA 4.0 8.5 CVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:N/VC:H/VI:L/VA:L/SC:H/SI:H/SA:H
CNA 4.0 8.5 CVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:N/VC:H/VI:L/VA:L/SC:H/SI:H/SA:H/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Affected products

  • logto-io logto

Classification

Weakness
  • CWE-918 Server-Side Request Forgery

References

Sources

Fencer Intel 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.

The maintainers of logto-io/logto published their own advisory on GitHub. Reviewed sources take precedence over it.