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BREW-aqtinstall-CVE-2026-23879 — py7zr: Arbitrary File Write Vulnerability

2026-10-06T07:17:48.864540+00:00

Affected: Homebrew: aqtinstall

### 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.

```python 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/someFi…

CVE-2026-23879 — py7zr: Arbitrary File Write Vulnerability

2026-10-06T07:17:48.864646+00:00

Affected: miurahr py7zr

py7zr is a Python-based library and utility to support 7zip archive compression, decompression, encryption and decryption. Versions 1.1.2 and below contain an an arbitrary file write vulnerability, 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. 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. 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. This issue has been fixed in version 1.1.3.

GHSA-q6rc-2cgv-63h7 — py7zr: Arbitrary File Write Vulnerability

2026-10-06T07:17:48.864683+00:00

Affected: PyPI: py7zr

### PoC #### **Construct PoC Archive File** The following pseudo-code illustrates the vulnerable logic.