CVE-2026-45695: Kopia: RCE via SSH ProxyCommand Injection

Should you act?

Critical and remotely reachable

No known exploitation yet, but it is network-reachable without credentials. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• No confirmed exploitation. It is not in CISA’s KEV catalog and CISA’s SSVC assessment records no known exploitation. That can change quickly after a public write-up; re-check if you are affected.
• EPSS 1.6%, percentile 76: FIRST’s model estimates a 1.6% chance of exploitation activity in the next 30 days, higher than 76% of all scored CVEs (moderate). EPSS is a probability, not a verdict.
• Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
• Only applies if your dependency tree includes github.com/kopia/kopia (Go) <= 0.22.3, fixed in 0.23.0. Check your lockfile, including transitive dependencies.

What it is

Kopia is a cross-platform backup tool for Windows, macOS, and Linux with fast incremental backups, client-side end-to-end encryption, compression, and data deduplication. Prior to 0.23.0, Kopia's HTTP server started with --without-password accepts unauthenticated requests to /api/v1/repo/exists and forwards attacker-supplied SFTP storage configuration to blob.NewStorage, where externalSSH: true and sshArguments containing -oProxyCommand= can cause exec.CommandContext("ssh") to invoke the command through OpenSSH. This issue is fixed in version 0.23.0.

From the GitHub advisory

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= token in sshArguments causes OpenSSH to invoke via $SHELL -c before any TCP connection is attempted, giving the requester arbitrary command execution as the Kopia process user.

Analysis

internal/server/serverauthzchecks.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.

Weakness type: CWE-78, CWE-306.

Product: github.com/kopia/kopia (Go) · Assigned by: GitHub_M · Published: 2026-07-16

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: low
• Privileges required: none (no login)
• User interaction: none
• Scope: unchanged

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

• CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
• CISA SSVC assessment: exploitation none, automatable yes, technical impact total.
• FIRST EPSS (model of 2026-10-21): 1.61% probability of exploitation activity in the next 30 days; percentile 76.

Timeline

• 2026-05-19 — GitHub-reviewed advisory GHSA-2q4c-3mrw-63c3 published (critical)
• 2026-07-16 — CVE record last updated
• 2026-07-16 — CVE record published by GitHub_M

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vulnerability records

1. GitHub Advisory GHSA-2q4c-3mrw-63c3 github.com
2. CVE.org record CVE-2026-45695 cve.org
3. NVD entry CVE-2026-45695 nvd.nist.gov

Other references from the CVE record and advisory

1. github.com github.com
2. github.com github.com
3. github.com github.com
4. github.com github.com

Critical Go advisories · Today’s Security Digest