Tarfile infinite loop during parsing with negative member offset

Basic Information

Title	Tarfile infinite loop during parsing with negative member offset
Type	cve
Published	2025-07-28T18:42:44.847Z
Modified	2025-07-28T19:30:55.878Z

Product Information

Vendor	Python Software Foundation
Product	CPython
Version	0

There is a defect in the CPython “tarfile” module affecting the “TarFile” extraction and entry enumeration APIs. The tar implementation would process tar archives with negative offsets without error, resulting in an infinite loop and deadlock during the parsing of maliciously crafted tar archives.

This vulnerability can be mitigated by including the following patch after importing the “tarfile” module:

import tarfile

def _block_patched(self, count):
    if count < 0: # pragma: no cover
        raise tarfile.InvalidHeaderError(“invalid offset”)
    return _block_patched._orig_block(self, count)

_block_patched._orig_block = tarfile.TarInfo._block
tarfile.TarInfo._block = _block_patched