rucio has an Authorization Bypass on REST API endpoint for signing URLs
Summary
The
/credentials/signurl endpoint decides authorization from the client-supplied
X-Rucio-Account HTTP header instead of the authenticated token's account. Any client holding
any valid auth token (even a low-privilege account they legitimately own) can send
X-Rucio-Account: root to pass the root-only permission check and have the Rucio server mint a presigned
read / write / delete URL for an
arbitrary object, signed with the RSE's stored S3 / GCS / Swift credentials.
Details
SignURL.get() takes the authorization principal from a request header and
never uses the token-authenticated identity:
# lib/rucio/web/rest/flaskapi/v1/credentials.py
account = request.headers.get('X-Rucio-Account', default=None) # L165 (attacker-controlled)
...
result = get_signed_url(account, rse=rse, service=service, # L194
operation=operation, url=url, lifetime=lifetime, vo=vo)
The gateway then uses that header value as the issuer for the permission check:
# lib/rucio/gateway/credential.py
auth_result = permission.has_permission(issuer=account, vo=vo, # L57
action='get_signed_url', kwargs=kwargs, ...)
and the permission function is root-only:
# lib/rucio/core/permission/generic.py
def perm_get_signed_url(issuer, kwargs, session):
return _is_root(issuer) # _is_root(x) -> x.external == 'root'
InternalAccount('root', vo).external == 'root' unconditionally, so the gate passes whenever the header is root. The endpoint is on AuthenticatedBlueprint, whose before_request hook validates the token and sets request.environ['issuer'] from the token — but nothing ever compares X-Rucio-Account to it:
# lib/rucio/web/rest/flaskapi/v1/common.py (request_auth_env)
flask.request.environ['issuer'] = auth.get('account') # L168 (the real account; unused by SignURL)
This is anomalous: every other authenticated handler derives the account from request.environ['issuer']; credentials.py is the only one that trusts the header. Additionally, core.credential.get_signed_url never checks that the supplied url's host/bucket belongs to the target RSE, so even a legitimate root caller gets an arbitrary-object signing oracle. In multi-VO the VO is also read from the X-Rucio-VO header, allowing cross-tenant targeting.
Proof of concept
Request (any valid token + spoofed account):
GET /credentials/signurl?rse=&svc=s3&op=delete&url=https://victim-bucket.s3.amazonaws.com/important/dataset.root HTTP/1.1
X-Rucio-Auth-Token:
X-Rucio-Account: root
Accept: application/octet-stream
Response:
200 OK with a presigned DELETE URL the attacker replays directly against the storage backend.
Impact
A low-privilege Rucio user can read, overwrite, and delete arbitrary objects on any cloud-backed (S3/GCS/Swift) RSE using the server's stored credentials — enabling data exfiltration, tampering, and destruction, and cross-tenant access in multi-VO deployments.
Credit
Reported by seankohjs. Found via static analysis + manual verification.
What the EG score is made of (scorer v4.0: the three questions the 0–10 score mixes, published apart · methodology)
The EG score (8.8): severity, escalated by confirmed exploitation. This CVE's 8.8 is its impact severity (EG Severity), not escalated.
- EG Severity
- 8.8 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