Partial path traversal in sharpcompress

CVE-2021-39208 → View on GitHub ↗ View on CVE.org ↗ View on NVD ↗

Description

SharpCompress recreates a hierarchy of directories under destinationDirectory if ExtractFullPath is set to true in options. In order to prevent extraction outside the destination directory the destinationFileName path is verified to begin with fullDestinationDirectoryPath. However it is not enforced that fullDestinationDirectoryPath ends with slash:

public static void WriteEntryToDirectory(IEntry entry,
                                         string destinationDirectory,
                                         ExtractionOptions? options,
                                         Action<string, ExtractionOptions?> write)
{
    string destinationFileName;
    string file = Path.GetFileName(entry.Key);
    string fullDestinationDirectoryPath = Path.GetFullPath(destinationDirectory);
...
        throw new ExtractionException("Entry is trying to write a file outside of the destination directory.");
}

If the destinationDirectory is not slash terminated like /home/user/dir it is possible to create a file with a name thats begins as the destination directory one level up from the directory, i.e. /home/user/dir.sh.

Impact

Because of the file name and destination directory constraints the arbitrary file creation impact is limited and depends on the use case.

Basic information

Type
reviewed
Severity
medium
Advisory on GitHub
Open advisory ↗
Repository advisory
Open repository advisory ↗
Source code
Browse source ↗
Published (advisory)
2021-09-20 19:53:42 UTC
Updated
2024-08-06 05:07:31 UTC
GitHub reviewed
2021-09-17 18:37:10 UTC
NVD published
2021-09-16

EPSS Score

Score Percentile
0.43% 62.52%

CVSS Scores

Base score Version Severity Vector
4.3 3.1 —
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:L/A:N Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:L)
A normal user session is enough; they don’t have to be admin.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:L)
Attackers could change some data, but it’s limited—not everything goes.
Availability (A:N)
Service keeps running; no real outage angle.
5.3 4.0 —
CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network.
Attack complexity (AC:L)
Exploitation conditions are straightforward and stable.
Attack requirements (AT:N)
No additional preconditions are required beyond normal reachability.
Privileges required (PR:L)
Low privileges are required.
User interaction (UI:N)
No user interaction is required.
Vulnerable system confidentiality impact (VC:N)
No confidentiality impact on the vulnerable system.
Vulnerable system integrity impact (VI:L)
Limited integrity impact on the vulnerable system.
Vulnerable system availability impact (VA:N)
No availability impact on the vulnerable system.
Subsequent system confidentiality impact (SC:N)
No confidentiality impact on subsequent systems.
Subsequent system integrity impact (SI:N)
No integrity impact on subsequent systems.
Subsequent system availability impact (SA:N)
No availability impact on subsequent systems.

Identifiers

Type Value
GHSA GHSA-jp7f-grcv-6mjf ↗
CVE CVE-2021-39208 ↗

CWEs

CWE id Name
CWE-22 Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')

Credits

  • JarLob (reporter)
  • geoffodonnell (analyst)

Affected packages (1)

Vulnerable version ranges and first patched releases as published by GitHub.

Ecosystem Package Vulnerable range First patched Vulnerable functions
nuget sharpcompress < 0.29 0.29 —

References

cvelogic Threat Intelligence