OAuthLib: Bearer token can be retrieved as long as client knows a valid client ID for device workflow
Summary
A call to the token endpoint with a grant type of
"urn:ietf:params:oauth:grant-type:device_code" and a bogus
device_code is able to get a bearer token as long as they know a valid client ID enabled for the device workflow.
Details
Section 3.4 of the RFC 8628 spec says that the token endpoint should take in device_code as a required parameter.DeviceCodeGrant.validate_token_request does not perform any validation of device_code. DeviceCodeGrant.validate_token_request should be validating that device_code was passed in as a parameter and that it is valid, similar to how AuthorizationCodeGrant.validate_token_request does the checks here and here.
I would like to propose a new method be added to RequestValidator called validate_device_code that is similar to the validate_code method and is called inside of DeviceCodeGrant.validate_token_request.
PoC
Create an implementation of
RequestValidation.authenticate_client that returns
True if the client's
client_type is
"public". You would find yourself in this scenario because there's another issue with
DeviceCodeGrant.validate_token_request where it doesn't properly handle public clients (see https://github.com/oauthlib/oauthlib/issues/919).
Create a client that has a client_type of "public" and set it's grant_type to "urn:ietf:params:oauth:grant-type:device_code".
With this implementation of RequestValidation.authenticate_client done, use that validator for your token endpoint. Call the token endpoint with a body of
{
"client_id": ,
"grant_type": "urn:ietf:params:oauth:grant-type:device_code",
"device_code":
}
You now have a bearer token for the client without a valid device_code.
Impact
Anyone using the RFC 8628 device workflow in oauthlib that doesn't realize the
device_code parameter is not being validated.
What the EG score is made of (scorer v4.0: the three questions the 0–10 score mixes, published apart · methodology)
The EG score (8.5): severity, escalated by confirmed exploitation. This CVE's 8.5 is its impact severity (EG Severity), not escalated.
- EG Severity
- 8.5 HIGHCVSS-B, impact only: no KEV listing, EPSS or EG-KEV tier raises it.GitHub Security Advisory CVSS
- EG Likelihood
- Unknown (no EPSS on record)Unknown, not low: FIRST has published no EPSS probability for this CVE.
- Confirmed exploitation
- None on record (CISA KEV, EG-KEV Tier 1)Reported apart from the likelihood: an observed fact, not a probability.
- EG Priority
- SSVC Track at medium mission impactTrack at low or medium mission impact; Track* at high (mission-essential systems).CISA BOD 26-04: 14 days if the affected system is publicly exposed; Fix on system upgrade if it is not.Each input and its source, and whom BOD 26-04 binds: the SSVC and BOD 26-04 blocks below.
SSVC (CISA's decision table, applied by EchelonGraph)Track at low or medium mission impact; Track* at high (mission-essential systems).
A fixed version is listed under Patch Availability. Apply it within your standard update timelines.
Exploitation none (no CISA value, KEV listing or exploit code on record) · Automatable no (CISA's BOD 26-04 default) · Technical impact total (CISA's BOD 26-04 default). EchelonGraph holds no SSVC assessment of this CVE from CISA: none of these inputs is from Vulnrichment. EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE. Mission impact is CISA's Mission & Well-being decision point, and only you can judge it. CISA's table makes it high when Mission Prevalence is Essential — the vulnerable component "directly provides capabilities that constitute at least one MEF for at least one entity" (MEF: mission essential function) — or when Public Well-Being Impact is Irreversible: "multiple fatalities are likely", the cyber-physical system "is likely lost or destroyed", "extreme or serious externalities" are imposed on other parties, or social systems such as elections or the financial grid "are destabilized and potentially collapse". CISA's decision table
BOD 26-04 (CISA's remediation timeline, Table 1)14 days if the affected system is publicly exposed; Fix on system upgrade if it is not.
The score's inputs: In CISA KEV no (CISA's KEV catalog) · Automatable no (CISA's BOD 26-04 default) · Technical impact total (CISA's BOD 26-04 default). Where an input reads “CISA's BOD 26-04 default”, no one has published it for this CVE, and CISA's implementation guidance says: “If “Automatable” and “Technical Impact” information items about a CVE ID are not available and the CVE ID is not in the KEV Catalog, CISA will treat its values as “no” and “total,” respectively, until CISA or a third party provides metadata about the CVE ID. CISA will always provide the Vulnrichment data for a CVE ID listed in the KEV Catalog.” Whether your system is publicly exposed is yours to answer. BOD 26-04 binds US Federal Civilian Executive Branch agencies; for anyone else it is CISA's published timeline, a reference rather than an obligation. The directive · how EchelonGraph applies it