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SSH host-key verification permanently disabled in Git mirror (SshGitMirror)

High
jrhee17 published GHSA-vjfw-cpmh-xwv3 Jun 22, 2026

Package

maven com.linecorp.centraldogma:centraldogma-server-mirror-git (Maven)

Affected versions

< 0.84.0

Patched versions

0.84.0

Description

Vulnerability

Central Dogma's Git mirror SSH client installs an Apache MINA SSHD ServerKeyVerifier lambda that returns true unconditionally for every outbound SSH connection used by git+ssh:// mirrors. The accompanying lines disable the known_hosts and ~/.ssh/config fallbacks, and a repo-wide search confirms that no host-key pinning mechanism (no acceptedHostKeys, knownHosts, KnownHostsServerKeyVerifier, StaticServerKeyVerifier, or RequiredServerKeyVerifier) exists anywhere in server-mirror-git/. Operators have no opt-in way to enable verification. Every outbound mirror connection blindly trusts whatever host key the remote presents.

Evidence

File: server-mirror-git/src/main/java/com/linecorp/centraldogma/server/internal/mirror/SshGitMirror.java
Lines 143-160 (especially 149) on branch main @ commit d64a5151:

private SshClient createSshClient() {
    final ClientBuilder builder = ClientBuilder.builder();
    // Do not use local file system.
    builder.hostConfigEntryResolver(HostConfigEntryResolver.EMPTY);   // line 146
    builder.fileSystemFactory(NoneFileSystemFactory.INSTANCE);        // line 147
    // Do not verify the server key.
    builder.serverKeyVerifier((clientSession, remoteAddress, serverKey) -> true);  // line 149
    ...
}

Verification:

  • Read confirmed on 2026-05-21 against main @ d64a5151.
  • A multi-agent code audit verified that no operator-facing pinning field exists on SshKeyCredential, PasswordCredential, or MirrorContext.
  • Exploit PoC reproduced locally with a paramiko-based fake SSH server bound to 127.0.0.1. The fake server presents an ephemeral RSA host key never seen before; the Central Dogma mirror client accepts the connection and proceeds to authentication, logging the offered username and public-key fingerprint. A correctly hardened SSH client would refuse the connection before reaching the authentication phase.
  • Full PoC artifacts (read-only, loopback-only) at ~/centraldogma-poc/C1_ssh_hostkey_bypass/ on the reporter's workstation.

Impact

Threat model: An on-path attacker on the corporate network — ARP spoofing on the LAN, internal DNS poisoning, malicious internal DNS overriding github.com or the configured internal git hostname, BGP hijack, sidecar/CNI compromise in Kubernetes, or any process able to answer TCP on the resolved IP. No Central Dogma account required; only network position.

  1. Direction LOCAL_TO_REMOTE: the attacker impersonating the remote git server receives the entire mirrored repository contents over the SSH session. Central Dogma is a configuration store, so this typically exfiltrates DB credentials, third-party API keys, certificates, feature flags, and any other secret configuration committed to mirrored repositories.
  2. Direction REMOTE_TO_LOCAL: the attacker can serve arbitrary commits which Central Dogma materializes into the local repo and then broadcasts to every subscribing microservice via the watch API. This is a supply-chain root-of-trust compromise across all downstream services consuming Central Dogma configuration.
  3. Credential theft chain with finding H2 (mirror credentials are not bound to a hostname): an SSH key or access token configured for github.com can be captured by the attacker's fake server and replayed against the real upstream, extending impact beyond Central Dogma itself.

Scope is Changed (CVSS) because exploitation alters trust assumptions of every downstream client of Central Dogma, not just Central Dogma itself.

How to fix

  1. Add an acceptedHostKeys: List<String> field to SshKeyCredential and PasswordCredential (or to MirrorContext). Values are SHA-256 fingerprints of trusted remote SSH server host keys, e.g. SHA256:nThbg6kXUpJWGl7E1IGOCspRomTxdCARLviKw6E5SY8.
  2. Replace the accept-all lambda at SshGitMirror.java:149 with a verifier that computes the SHA-256 fingerprint of the presented host key and compares it against the credential's allowlist using a constant-time comparison.
  3. Refuse to connect when acceptedHostKeys is empty — fail-closed. Do not implement implicit TOFU.
  4. Optionally provide an admin-only dogma mirror probe-host-key <remote> tool that performs a single audited connection, prints the server's fingerprint, and prompts the operator to add it to the credential. This makes TOFU an explicit, audited operation.
  5. Update SshGitMirrorTest.java and it/mirror/* tests to pin a test fingerprint or use the explicit trust-once tool, so the regression cannot silently return.

Severity

High

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 Adjacent
Attack Complexity Low
Attack Requirements Present
Privileges Required None
User interaction None
Vulnerable System Impact Metrics
Confidentiality High
Integrity High
Availability None
Subsequent System Impact Metrics
Confidentiality High
Integrity High
Availability Low

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:A/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:N/SC:H/SI:H/SA:L

CVE ID

CVE-2026-11745

Weaknesses

Key Exchange without Entity Authentication

The product performs a key exchange with an actor without verifying the identity of that actor. Learn more on MITRE.