GHSA-2q4c-3mrw-63c3 is a critical-severity (CVSS 9.8) OS Command Injection vulnerability in github.com/kopia/kopia. A fix is available for github.com/kopia/kopia — see the affected versions and patch details below.
Kopia: RCE via SSH ProxyCommand Injection
Exploitation Status
No confirmed exploitation observed yet
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- A successful exploit gives an attacker total control of the affected component, not partial access.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for GHSA-2q4c-3mrw-63c3.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
GHSA-2q4c-3mrw-63c3 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 380,526 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
Real-World Exposure
github.com/kopia/kopiaReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.
Description
Summary
Kopia's HTTP server, when started with --without-password , accepts unauthenticated requests to /api/v1/repo/exists. The handler forwards an attacker-supplied storage configuration to blob.NewStorage. For SFTP backends with externalSSH: true, that path constructs a process command line by splitting sshArguments on spaces and passes the result directly to exec.CommandContext("ssh"). An -oProxyCommand=<cmd> token in sshArguments causes OpenSSH to invoke <cmd> via $SHELL -c before any TCP connection is attempted, giving the requester arbitrary command execution as the Kopia process user.
Analysis
internal/server/server_authz_checks.go lines 61–73:
when the server is started without --server-username or --server-password, getAuthenticator() returns nil and requireUIUser unconditionally authorizes the request. Every endpoint registered through handleUIPossiblyNotConnected becomes accessible without credentials.
repo/blob/sftp/sftp_storage.go lines 448–468:
opt.SSHArguments is populated from the JSON request body (storage.config.sshArguments). The string is split only on the literal ASCII space character, there is no shell style tokenizer, no quote handling, and no allowlist. Whatever tokens the caller supplies are appended to the ssh argv.
OpenSSH treats -oProxyCommand=<value> as a directive to execute <value> via the user's shell ($SHELL -c <value>) and pipe the SSH transport over its stdio. The shell invocation happens before SSH attempts a TCP connection, so the command runs even when the target host is unreachable.
Impact
No user interaction is required. No valid credentials are required. The exploit is a single HTTP request.
Credits
This vulnerability was discovered and responsibly disclosed by Daniele Berardinelli.
Mitigation
https://github.com/kopia/kopia/pull/5354 disallows starting of a server without a password which also listens on a non-loopback interface.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹Go | github.com/kopia/kopia | all versions | 0.23.0go get github.com/kopia/kopia@v0.23.0 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/kopia/kopia, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update github.com/kopia/kopia to 0.23.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-2q4c-3mrw-63c3 is resolved across your whole dependency graph.
Workarounds
Stop passing untrusted input into the interpreter or shell: call the affected binary with an argument array rather than a composed command string, reject anything outside a strict allowlist of expected values, and run the component under an account that cannot reach beyond the work it legitimately does.
How to detect GHSA-2q4c-3mrw-63c3
A community-maintained Nuclei template exists for this CVE. You can scan for it directly:
nuclei -id ghsa-2q4c-3mrw-63c3 -u https://target- Template
- Kopia Server 0.23.0 - Remote Code Execution
- Severity
- critical
- Impact
- An unauthenticated attacker can execute arbitrary commands as the Kopia server process (often root in a container), leading to full host compromise and access to all managed backup data.
- Remediation
- Upgrade to Kopia 0.23.0 or later, which refuses to bind an unauthenticated server to a non-loopback address. Do not expose the server with --without-password on untrusted networks.
Template by ProjectDiscovery nuclei-templates (kenlacroix), MIT licensed. View the full template. Scan only systems you are authorised to test.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
Red Hat Product Security considers this bug as Moderate as this requires active change of out of box configaration for this bug to be exploitable. There is no common use case under which Kopia HTTP server should be started without a password. The diecrepancy in CVSS scores between Red Hat and NVD comes from the…
This bug can be rendered unusable by making sure that --without-password is not included in startup options for Kopia HTTP server.Source: Red Hat security advisory for GHSA-2q4c-3mrw-63c3 (CC BY 4.0)
Frequently Asked Questions
Is GHSA-2q4c-3mrw-63c3 in your dependencies?
Find it across Go, including transitive dependencies.