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oras-go: Malicious registry can hijack Bearer token realm to exfiltrate credentials and refresh tokens

Low severity GitHub Reviewed Published Jun 11, 2026 in oras-project/oras-go • Updated Jul 1, 2026

Package

gomod oras.land/oras-go (Go)

Affected versions

<= 1.2.7

Patched versions

None
gomod oras.land/oras-go/v2 (Go)
< 2.6.1
2.6.1

Description

Summary

oras-go's auth.Client follows the realm URL from a registry's WWW-Authenticate: Bearer challenge without validating its scheme or host. The realm field is server-controlled by design in the OCI/distribution spec — registries legitimately point token requests at a separate auth endpoint (e.g. Docker Hub's registry-1.docker.io -> auth.docker.io), so cross-host realms on public DNS names are not in themselves a vulnerability. Two specific patterns, however, are never legitimate under any registry trust model and can be abused by a malicious or compromised registry (or a man-in-the-middle on a plaintext connection):

  1. SSRF to internal networks. A realm of http://169.254.169.254/... (AWS/Azure IMDS), http://10.0.0.x/... (RFC 1918), or http://127.0.0.1/... causes oras-go running on a cloud VM or corporate workstation to issue outbound HTTP requests from inside the user's trust boundary to an endpoint the user did not choose. The user's stored credentials are attached to those requests, but the principal harm is the network primitive — probing internal endpoints from the client. On IMDSv1 the response body is recoverable from log channels; on IMDSv2 the probe itself can still be used for service discovery.

  2. TLS downgrade. A registry contacted over https:// can return a realm with an http:// scheme, causing oras-go to send the user's credentials over plaintext to the token endpoint. This defeats the transport security the user chose when typing https://.

What is NOT claimed

This advisory does not claim that credential forwarding to an arbitrary public attacker host through a server-controlled realm is, on its own, a vulnerability. The distribution spec defines realm as a server-controlled field; a strict same-host or same-eTLD+1 enforcement would deviate from the spec and break legitimate split-host deployments. Operators who want defense-in-depth against cross-host realm forwarding can use the opt-in Client.TrustedRealmHosts allowlist (added separately).

Affected versions

oras.land/oras-go/v2 <= v2.6.0

Severity

Medium. Network attack vector, low complexity, no privileges required, user interaction required (victim runs an oras command against the malicious or MITM'd registry), unchanged scope. Confidentiality impact is limited — IMDS probe responses can disclose information, and TLS downgrade exposes the realm request to passive observers — but the attacker does not obtain credentials beyond what the malicious endpoint already controls.

Affected code

  • registry/remote/auth/client.go — Client.Do() (bearer challenge handling)
  • registry/remote/auth/client.go — Client.fetchBearerToken() / fetchDistributionToken / fetchOAuth2Token

The realm parameter from parseChallenge is threaded through to http.NewRequestWithContext without scheme or host validation.

CWE

  • CWE-918: Server-Side Request Forgery (SSRF)
  • CWE-319: Cleartext Transmission of Sensitive Information

Patch

registry/remote/auth/client.go now rejects realm URLs that:

  • use a scheme other than http or https
  • use http when the registry was contacted over https (TLS downgrade)
  • use an IP literal in a loopback, link-local, private, or unspecified range, unless the registry itself was reached at the same hostname (so loopback / in-cluster deployments are unaffected)

Cross-host realms on public DNS names continue to be accepted.

Credit

Reported by bugbunny.ai.

References

@TerryHowe TerryHowe published to oras-project/oras-go Jun 11, 2026
Published to the GitHub Advisory Database Jul 1, 2026
Reviewed Jul 1, 2026
Last updated Jul 1, 2026

Severity

Low

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v4 base metrics

Exploitability Metrics
Attack Vector Network
Attack Complexity High
Attack Requirements None
Privileges Required None
User interaction Active
Vulnerable System Impact Metrics
Confidentiality Low
Integrity None
Availability None
Subsequent System Impact Metrics
Confidentiality None
Integrity None
Availability None

CVSS v4 base metrics

Exploitability Metrics
Attack Vector: This metric reflects the context by which vulnerability exploitation is possible. This metric value (and consequently the resulting severity) will be larger the more remote (logically, and physically) an attacker can be in order to exploit the vulnerable system. The assumption is that the number of potential attackers for a vulnerability that could be exploited from across a network is larger than the number of potential attackers that could exploit a vulnerability requiring physical access to a device, and therefore warrants a greater severity.
Attack Complexity: This metric captures measurable actions that must be taken by the attacker to actively evade or circumvent existing built-in security-enhancing conditions in order to obtain a working exploit. These are conditions whose primary purpose is to increase security and/or increase exploit engineering complexity. A vulnerability exploitable without a target-specific variable has a lower complexity than a vulnerability that would require non-trivial customization. This metric is meant to capture security mechanisms utilized by the vulnerable system.
Attack Requirements: This metric captures the prerequisite deployment and execution conditions or variables of the vulnerable system that enable the attack. These differ from security-enhancing techniques/technologies (ref Attack Complexity) as the primary purpose of these conditions is not to explicitly mitigate attacks, but rather, emerge naturally as a consequence of the deployment and execution of the vulnerable system.
Privileges Required: This metric describes the level of privileges an attacker must possess prior to successfully exploiting the vulnerability. The method by which the attacker obtains privileged credentials prior to the attack (e.g., free trial accounts), is outside the scope of this metric. Generally, self-service provisioned accounts do not constitute a privilege requirement if the attacker can grant themselves privileges as part of the attack.
User interaction: This metric captures the requirement for a human user, other than the attacker, to participate in the successful compromise of the vulnerable system. This metric determines whether the vulnerability can be exploited solely at the will of the attacker, or whether a separate user (or user-initiated process) must participate in some manner.
Vulnerable System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the VULNERABLE SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the VULNERABLE SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the VULNERABLE SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
Subsequent System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the SUBSEQUENT SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the SUBSEQUENT SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the SUBSEQUENT SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:A/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N

EPSS score

Weaknesses

Cleartext Transmission of Sensitive Information

The product transmits sensitive or security-critical data in cleartext in a communication channel that can be sniffed by unauthorized actors. Learn more on MITRE.

Server-Side Request Forgery (SSRF)

The web server receives a URL or similar request from an upstream component and retrieves the contents of this URL, but it does not sufficiently ensure that the request is being sent to the expected destination. Learn more on MITRE.

CVE ID

CVE-2026-48978

GHSA ID

GHSA-xf85-363p-868w

Source code

Credits

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