EUVD-2026-72539Severity by source
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:N/SC:L/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
DNS control requirement raises AC to H; SSRF reaches other systems (S:C); only subsequent confidentiality probing (C:L), no integrity or availability impact.
Primary rating from Vendor (EEF).
CVSS VectorVendor: EEF
Lifecycle Timeline
2DescriptionCVE.org
Server-Side Request Forgery (SSRF) vulnerability in ash-project ash_authentication_oauth2_server allows an attacker who controls a client metadata URL and its DNS to make the server connect to internal or loopback addresses.
public_ip?/1 in AshAuthentication.Oauth2Server.CIMD.ReqFetcher enforces the outbound policy for CIMD metadata fetches. It classified several address forms as publicly routable that are not: IPv4-compatible ::/96 (for example ::127.0.0.1), SIIT IPv4-translated ::ffff:0:0:0/96, and deprecated site-local fec0::/10. A returned AAAA record in one of these ranges passed the policy, so a fetch pinned to that address reached space the policy was meant to block.
This issue affects ash_authentication_oauth2_server: from 0.3.0 before 0.3.1.
AnalysisAI
SSRF in ash_authentication_oauth2_server 0.3.0 allows an attacker who controls both an OAuth2 client's metadata URL and the associated DNS resolution to route the server's outbound CIMD metadata fetches to loopback, link-local, or internal addresses. The public_ip?/1 guard in AshAuthentication.Oauth2Server.CIMD.ReqFetcher failed to classify three IPv6 address families as private - IPv4-compatible ::/96 (e.g., ::127.0.0.1), SIIT IPv4-translated ::ffff:0:0:0/96, and deprecated site-local fec0::/10 - so a crafted DNS AAAA response in any of these ranges bypassed the policy. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Exploitation requires two specific preconditions: (1) the attacker must be able to supply or influence an OAuth2 client's metadata URL - either by registering a new client if dynamic registration is open, or by compromising an existing client registration - because the vulnerability is only triggered during CIMD metadata fetches; and (2) the attacker must control DNS resolution for the metadata URL hostname to serve a crafted AAAA record in the ::/96, ::ffff:0:0:0/96, or fec0::/10 IPv6 ranges. … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | The vendor-supplied CVSS 4.0 score of 6.3 (AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:N/SC:L/SI:N/SA:N) accurately captures the threat profile. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | Full exploit scenario with step-by-step reproduction available after sign-in. |
| Remediation | Upgrade ash_authentication_oauth2_server to version 0.3.1, which includes fix commit 268b591261a3473ab9b87272963e4dd2fd99d972 correcting the IPv6 address classification logic. … Detailed patch versions, workarounds, and compensating controls in full report. |
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Multi-tenant OAuth2 metadata cross-tenant leakage in ash_authentication_oauth2_server (versions 0.1.3 through before 0.3
Same weakness CWE-918 – Server-Side Request Forgery (SSRF)
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External POC / Exploit Code
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