Obot before v0.23.0 Authentication Bypass via OAuth Dynamic Client Registration

CISA KEV is observed exploitation evidence. FIRST EPSS is a dated prediction of exploitation in the next 30 days. Missing scores are unknown. This collector requests predictions only for explicit CVE aliases in the public NuGet archive; Microsoft release views retain their existing prediction scope.

No collected risk observation for these identifiers. This does not establish absence of exploitation or a zero probability.

Obot before v0.23.0 (affected versions <= v0.22.1) running with OBOT_SERVER_ENABLE_AUTHENTICATION=true exposes OAuth dynamic client registration without authentication and without any restriction on the redirect URIs a client may register. Because the authorization flow auto-completes for an already logged-in user with no consent screen, an attacker who registers a client pointing at their own domain and induces a logged-in victim to visit a single crafted authorization URL receives an authorization code at the attacker-controlled redirect URI and can exchange it for an access token and refresh token. The token minted by the MCP OAuth flow carries the victim's full group set in the JWT, and Obot validated only the issuer and not the audience, so the token is accepted as a bearer token against any Obot API endpoint the victim can access rather than being scoped to the requested MCP server, allowing the attacker to read or modify the victim's resources until the token is revoked. v0.23.0 adds a consent screen, restricts MCP OAuth tokens to the MCP involved in the request, and enforces audience validation.

Source published

27 Sep 2026 20:49:54 UTC

Source modified

30 Sep 2026 22:11:52 UTC

Observed here

23 Oct 2026 15:48:27 UTC

Source terms

CVE Program Terms of Use

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CVSS 4.0 · 8.7 CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

CVSS 3.1 · 8.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

Obot before v0.23.0 (affected versions <= v0.22.1) running with OBOT_SERVER_ENABLE_AUTHENTICATION=true exposes OAuth dynamic client registration without authentication and without any restriction on the redirect URIs a client may register. Because the authorization flow auto-completes for an already logged-in user with no consent screen, an attacker who registers a client pointing at their own domain and induces a logged-in victim to visit a single crafted authorization URL receives an authorization code at the attacker-controlled redirect URI and can exchange it for an access token and refresh token. The token minted by the MCP OAuth flow carries the victim's full group set in the JWT, and Obot validated only the issuer and not the audience, so the token is accepted as a bearer token against any Obot API endpoint the victim can access rather than being scoped to the requested MCP server, allowing the attacker to read or modify the victim's resources until the token is revoked. v0.23.0 adds a consent screen, restricts MCP OAuth tokens to the MCP involved in the request, and enforces audience validation.

Source published

Sep 27, 2026, 8:49:54 PM (timezone not stated)

Source modified

Sep 30, 2026, 10:11:52 PM (timezone not stated)

Observed here

11 Nov 2026 05:27:58 UTC

Source terms

ENISA EUVD · source terms and attribution apply

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: euvd · ENISA EUVD · source terms and attribution apply. Source text is retained; field grouping and change labels are provided by ChangeIntel.

EUVD CVSS 4.0 · 8.7 CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

Obot before v0.23.0 (affected versions <= v0.22.1) running with OBOT_SERVER_ENABLE_AUTHENTICATION=true exposes OAuth dynamic client registration without authentication and without any restriction on the redirect URIs a client may register. Because the authorization flow auto-completes for an already logged-in user with no consent screen, an attacker who registers a client pointing at their own domain and induces a logged-in victim to visit a single crafted authorization URL receives an authorization code at the attacker-controlled redirect URI and can exchange it for an access token and refresh token. The token minted by the MCP OAuth flow carries the victim's full group set in the JWT, and Obot validated only the issuer and not the audience, so the token is accepted as a bearer token against any Obot API endpoint the victim can access rather than being scoped to the requested MCP server, allowing the attacker to read or modify the victim's resources until the token is revoked. v0.23.0 adds a consent screen, restricts MCP OAuth tokens to the MCP involved in the request, and enforces audience validation.

Source published

27 Sep 2026 21:17:01 UTC

Source modified

30 Sep 2026 23:16:57 UTC

Observed here

25 Oct 2026 04:17:26 UTC

Source terms

NIST NVD usage terms; underlying source attribution retained

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: nvd · NIST NVD usage terms; underlying source attribution retained. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 4.0 · [email protected] · Secondary · 8.7 CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/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

CVSS 3.1 · [email protected] · Secondary · 8.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

## Summary In affected versions, an unauthenticated attacker could register an OAuth client with an arbitrary external redirect URI, and the authorization flow would auto-complete without a consent screen. If a logged-in victim visited a crafted authorization URL, an authorization code was delivered to the attacker's redirect URI and exchanged for an access token. That token was minted with the victim's full set of groups, so it could be used as a bearer token against the Obot API endpoints the victim had access to — rather than being scoped to just the requested MCP server. ## Am I affected? You are affected if you run Obot `<= v0.22.1` with `OBOT_SERVER_ENABLE_AUTHENTICATION=true`. Exploitation requires a logged-in victim to visit a single attacker-controlled authorization URL. ## Details Three issues combined to create this vulnerability. First, OAuth dynamic client registration was reachable without authentication and applied no restriction on the redirect URIs a client could register, so an attacker could register a client pointing at their own domain. The authorization flow then auto-completed for an already-logged-in user with no consent step, so simply loading the authorization URL issued an authorization code and redirected it to the attacker's URI. Finally, the token minted by the MCP OAuth flow carried the victim's full group set in the JWT — the field used to authorize API paths — so although the token's audience was the requested MCP server, it was accepted across the victim's wider API access. (Obot's JWT verification validated the issuer but not the audience; audiences were enforced at the MCP layer.) ## Impact Worst case is that an attacker who gets a logged-in victim to click a crafted link obtains an access token (and refresh token) usable against the API endpoints the victim is authorized for — reading or modifying the victim's resources until the token is revoked. No attacker-side privileges are required. ## Mitigation Upgrade to **v0.23.0** or later, which adds three protections: a consent screen that shows the requesting client and the MCP server it wants access to before authorization completes; restriction of tokens minted by the MCP OAuth flow to only the MCP involved in the request, so they can no longer reach the user's wider API access; and audience validation as a fail-safe ensuring these tokens are only accepted for the MCP server they were issued for. ## Severity CVSS v3.1 Score: **8.8/10 (High)** — `CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H` ## Credits The Obot team would like to thank [@EQSTLab](https://github.com/EQSTLab) for responsibly disclosing this issue in accordance with our [security policy](https://github.com/obot-platform/obot/?tab=security-ov-file).

Source published

18 Sep 2026 17:59:35 UTC

Source modified

28 Sep 2026 17:10:41 UTC

Observed here

24 Oct 2026 13:19:41 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

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CVSS_V3 · CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

Publisher rating · HIGH

Obot: OAuth Dynamic Client Registration Enables API Token Theft via Audience Confusion in github.com/obot-platform/obot

Source published

28 Sep 2026 16:43:40 UTC

Source modified

28 Sep 2026 17:10:41 UTC

Observed here

24 Oct 2026 13:19:41 UTC

Source terms

OSV · upstream source license applies

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · OSV · upstream source license applies. Source text is retained; field grouping and change labels are provided by ChangeIntel.