CVE-2026-49349: regclient Credential Leak Vulnerability

CVE-2026-49349 Overview

CVE-2026-49349 affects regclient, a Docker and Open Container Initiative (OCI) Registry Client written in Go. Versions prior to 0.11.5 may inadvertently transmit registry credentials to external servers when pulling foreign blobs. The vulnerability is classified under CWE-522: Insufficiently Protected Credentials.

Exploitation requires a malicious registry server, a malicious blob store, or a registry that does not restrict external URLs for foreign blobs. Successful attacks disclose authentication credentials tied to the victim's registry session. Version 0.11.5 resolves the flaw.

Critical Impact
Attackers operating a malicious registry or blob store can harvest regclient user credentials, enabling downstream access to private container images and registry accounts.

Affected Products

regclient versions prior to 0.11.5
Container build pipelines integrating regclient libraries (regctl, regsync, regbot)
CI/CD workflows using regclient to pull foreign blob references

Discovery Timeline

2026-08-12 - CVE-2026-49349 published to the National Vulnerability Database (NVD)
2026-08-12 - Last updated in NVD database
Fix released in regclient version 0.11.5 per the GitHub Security Advisory

Technical Details for CVE-2026-49349

Vulnerability Analysis

regclient handles container image manifests that reference foreign blobs, which are layer objects hosted outside the primary registry. The OCI specification permits manifest entries to include external URLs pointing to alternate blob locations. When regclient followed these URLs, it reused authentication headers associated with the originating registry session.

This behavior violates credential scoping expectations. A registry operator can craft manifests that reference URLs on attacker-controlled infrastructure. When a victim pulls the image, regclient forwards the bearer token or basic-auth header to the external endpoint, exposing the secret to the third party.

The issue is a credential-handling defect rather than a memory-safety flaw. It requires user interaction because a user must initiate a pull against the malicious manifest. Once triggered, the attacker captures credentials with no additional victim involvement.

Root Cause

The root cause is the absence of a check that isolates authentication material to the registry host that issued it. regclient did not enforce an origin boundary when redirecting requests to foreign blob URLs, allowing bearer tokens and other credentials to accompany requests to arbitrary hosts.

Attack Vector

The attack requires network access to a malicious registry, a malicious blob store, or a registry that fails to restrict external foreign blob URLs. The attacker publishes a manifest whose foreign layer references an attacker-controlled host. When the victim runs regctl image copy or similar operations, regclient contacts the external URL and includes the credential header. The attacker's server logs the request and extracts the credentials for reuse.

Code examples are not published because no verified exploit proof-of-concept is available. Refer to the GitHub Security Advisory GHSA-qvqc-4c52-x6qp for maintainer-provided technical detail.

Detection Methods for CVE-2026-49349

Indicators of Compromise

Outbound HTTP or HTTPS requests from build agents to registry hosts not present in an approved allow-list
Presence of Authorization: Bearer or Authorization: Basic headers in traffic to unexpected external endpoints
regclient binaries or libraries with versions prior to 0.11.5 in build and runtime environments

Detection Strategies

Inventory container tooling to identify regctl, regsync, and regbot binaries and their versions
Inspect image manifests for foreign layer entries with urls fields referencing untrusted domains
Correlate registry authentication events with unusual downstream network destinations from CI/CD runners

Monitoring Recommendations

Log egress traffic from build systems and alert on connections to hosts outside the registry allow-list
Monitor registry access logs for token reuse from unexpected source addresses, indicating credential exfiltration
Track version metadata for regclient components in software bills of materials (SBOMs)

How to Mitigate CVE-2026-49349

Immediate Actions Required

Upgrade all regclient installations to version 0.11.5 or later
Rotate any registry credentials, tokens, or service account keys that may have been used with vulnerable regclient versions against untrusted registries
Audit CI/CD pipelines for pulls from registries controlled by external parties

Patch Information

regclient version 0.11.5 fixes the credential leak by restricting credential propagation when accessing foreign blob URLs. Update via the project's release channel or rebuild container images and pipelines to include the patched binary. See the regclient security advisory for release notes.

Workarounds

Restrict regclient usage to trusted registries under organizational control until the upgrade is complete
Configure network egress policies on build hosts to block outbound requests to domains outside an approved registry list
Use short-lived, scoped registry tokens to limit the window of exposure if a credential is leaked

bash

# Verify the installed regclient version and upgrade
regctl version
# Download the patched release (replace URL with the official 0.11.5 asset)
curl -L -o regctl https://github.com/regclient/regclient/releases/download/v0.11.5/regctl-linux-amd64
chmod 755 regctl
./regctl version