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GHSA-2q4c-3mrw-63c3
No affected components available
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.
The vulnerability can be exploited over the network without needing physical access. It is easy for an attacker to exploit this vulnerability. An attacker does not need any special privileges or access rights. No user interaction is needed for the attacker to exploit this vulnerability. The impact is confined to the system where the vulnerability exists. There is a high impact on the confidentiality of the information. There is a high impact on the integrity of the data. There is a high impact on the availability of the system.
Active exploitation in the wild has been confirmed. Immediate patching or mitigation is required.
The exploit probability is very low. The vulnerability is unlikely to be exploited in the next 30 days.
We did not find any exploit available. Neither in GitHub repositories nor in the Exploit-Database.
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