[3.14] gh-151497: Avoid huge pre-allocation for oversized tarfile extended headers (GH-151498)#151979
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…nded headers (pythonGH-151498) tarfile reads a member's extended header (a GNU long name/link or a pax header) with a single read sized by the header's size field: buf = tarfile.fileobj.read(self._block(self.size)) The size is taken from the archive and is not validated, so a ~512-byte crafted file can claim several gigabytes (or, via base-256 encoding, far more) and make read() pre-allocate that much memory -- on open/iterate, before any extraction filter runs. Read the extended-header data in bounded chunks instead, so an oversized or truncated header can no longer force a huge allocation. The bytes returned for valid archives are unchanged. (cherry picked from commit da99711) Co-authored-by: Shardul Deshpande <iamsharduld@users.noreply.github.com>
This was referenced Jun 23, 2026
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tarfile reads a member's extended header (a GNU long name/link or a pax
header) with a single read sized by the header's size field:
The size is taken from the archive and is not validated, so a ~512-byte
crafted file can claim several gigabytes (or, via base-256 encoding, far
more) and make read() pre-allocate that much memory -- on open/iterate,
before any extraction filter runs.
Read the extended-header data in bounded chunks instead, so an oversized
or truncated header can no longer force a huge allocation. The bytes
returned for valid archives are unchanged.
(cherry picked from commit da99711)
Co-authored-by: Shardul Deshpande iamsharduld@users.noreply.github.com