Arbitrary File Write via Archive Extraction (Zip Slip)

Affecting github.com/u-root/u-root/pkg/tarutil package, versions *

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Overview

github.com/u-root/u-root/pkg/tarutil is a package that provides Go versions of standard Linux tools and bootloaders. It also provides tools for compiling Go programs in a single binary and creating initramfs images.

Affected versions of this package are vulnerable to Arbitrary File Write via Archive Extraction (Zip Slip). It is vulnerable to both leading and non-leading relative path traversal attacks in tar file extraction.

PoC

package main

import (
    "os"
    "fmt"
    tar "github.com/u-root/u-root/pkg/tarutil"
)


func main() {
    file := "relative.tar"
    f, err := os.Open(file)
    if err != nil {
        fmt.Println(err)
    }
    defer f.Close()

    if err := tar.ExtractDir(f, "."); err != nil {
        fmt.Println(err)
    }
}

with "relative.tar" being a tar archive that includes a file with filepath that uses leading or non-leading "../" .

Details

It is exploited using a specially crafted zip archive, that holds path traversal filenames. When exploited, a filename in a malicious archive is concatenated to the target extraction directory, which results in the final path ending up outside of the target folder. For instance, a zip may hold a file with a "../../file.exe" location and thus break out of the target folder. If an executable or a configuration file is overwritten with a file containing malicious code, the problem can turn into an arbitrary code execution issue quite easily.

The following is an example of a zip archive with one benign file and one malicious file. Extracting the malicous file will result in traversing out of the target folder, ending up in /root/.ssh/ overwriting the authorized_keys file:


+2018-04-15 22:04:29 ..... 19 19 good.txt

+2018-04-15 22:04:42 ..... 20 20 ../../../../../../root/.ssh/authorized_keys

Remediation

There is no fixed version for github.com/u-root/u-root/pkg/tarutil.

References

CVSS Score

7.5
high severity
  • Attack Vector
    Network
  • Attack Complexity
    Low
  • Privileges Required
    None
  • User Interaction
    None
  • Scope
    Unchanged
  • Confidentiality
    None
  • Integrity
    High
  • Availability
    None
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
Credit
Georgios Gkitsas of Snyk Security Team
CVE
CVE-2020-7669
CWE
CWE-22
Snyk ID
SNYK-GOLANG-GITHUBCOMUROOTUROOTPKGTARUTIL-570428
Disclosed
01 Sep, 2020
Published
01 Sep, 2020