anthropics/skills · error · ValueError

unsafe archive entry: {m.filename!r}

Error message

unsafe archive entry: {m.filename!r}

What it means

pptx copy of the zip-slip escape guard (same as error 7): safe_extract() resolves each member's destination path and raises if it falls outside the extraction directory — absolute entry names ('/etc/x') or '..' traversal. This blocks arbitrary-file overwrite during unpack of hostile or malformed archives.

Source

Thrown at skills/pptx/scripts/office/helpers/__init__.py:81

def part_text(data: bytes) -> str:
    return data.decode("utf-8", "surrogateescape")


XML_SPACE = " \t\r\n"


def rendered_text(text: str, preserve: bool) -> str:
    return text if preserve else text.strip(XML_SPACE)


def safe_extract(zf: zipfile.ZipFile, dest: Path) -> None:
    dest = dest.resolve()
    for m in zf.infolist():
        if stat.S_ISLNK(m.external_attr >> 16):
            raise ValueError(f"symlink archive entry not allowed: {m.filename!r}")
        target = (dest / m.filename).resolve()
        if not target.is_relative_to(dest):
            raise ValueError(f"unsafe archive entry: {m.filename!r}")
        zf.extract(m, dest)


def rezip(src_dir: Path, out_path: Path) -> None:
    files = sorted(p for p in src_dir.rglob("*") if p.is_file())
    ct = src_dir / "[Content_Types].xml"
    fd, tmp_name = tempfile.mkstemp(
        prefix=out_path.name + ".", suffix=".tmp", dir=out_path.parent
    )
    tmp_out = Path(tmp_name)
    try:
        with os.fdopen(fd, "wb") as fh:
            with zipfile.ZipFile(fh, "w", zipfile.ZIP_DEFLATED) as zf:
                if ct.exists():
                    zf.write(ct, ct.relative_to(src_dir), compress_type=zipfile.ZIP_STORED)
                for f in files:
                    if f == ct:
                        continue

View on GitHub (pinned to f6656c1256)

Solutions

1. Reject/quarantine the file — the guard fired on a genuinely dangerous entry name.
2. If the entry name is corruption fallout, rebuild the archive with clean relative names.
3. Pre-scan archives for absolute or '..' names before processing.
4. Restrict the pipeline to trusted .pptx sources.

Example fix

# pre-scan gate
import zipfile
def escapes(path):
    with zipfile.ZipFile(path) as zf:
        return any(n.startswith("/") or ".." in n.split("/") for n in zf.namelist())
if escapes(upload):
    raise ValueError("reject archive with escaping entries")

import zipfile

def has_escaping_entries(path: str) -> bool:
    with zipfile.ZipFile(path) as zf:
        return any(n.startswith("/") or n.startswith("\\") or ".." in n.replace("\\", "/").split("/") for n in zf.namelist())

from office.helpers import safe_extract
try:
    safe_extract(zf, dest)
except ValueError as e:
    if "unsafe archive entry" in str(e):
        quarantine(path)  # zip-slip; no fallback extraction
    else:
        raise

When it happens

Trigger: Unpacking an archive containing an entry named '/tmp/evil' or '../../../home/u/.bashrc'; also non-OOXML zips mistakenly fed to the pptx unpack flow.

Common situations: Malicious uploads; corrupted zip central directories producing mangled names; archives from unreliable sources.

Related errors

• symlink archive entry not allowed: {m.filename!r}
• unsafe archive entry: {m.filename!r}
• symlink archive entry not allowed: {m.filename!r}
• unsafe archive entry: {m.filename!r}
• relationship target escapes the package: {target!r}

AI-assisted analysis of anthropics/skills@f6656c1256 (2026-08-14). Data as JSON: /api/errors/0157a514acbdcdab. Report an issue: GitHub.