anthropics/skills · error · ValueError

symlink archive entry not allowed: {m.filename!r}

Error message

symlink archive entry not allowed: {m.filename!r}

What it means

safe_extract() refuses to extract any archive member whose Unix mode bits (external_attr >> 16) indicate a symbolic link. Extracting symlinks from an OOXML zip would allow a crafted archive to place links that redirect later writes outside the destination — a zip-slip variant — so extraction aborts before writing anything for that entry. Present in both docx and pptx office/helpers.

Source

Thrown at skills/docx/scripts/office/helpers/__init__.py:78

    return posixpath.join(owner_dir.as_posix(), rels_file.name[: -len(".rels")]).lstrip("./")


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)

View on GitHub (pinned to f6656c1256)

Solutions

1. Treat the file as untrusted: reject/quarantine it — the guard is doing its job.
2. If you control the archive, rebuild it without symlinks: unzip normally (with symlink conversion off), then rezip the plain files.
3. Scan the package before processing: for m in ZipFile(f).infolist(): reject if stat.S_ISLNK(m.external_attr >> 16).
4. Determine which upstream producer created the symlink entry and fix that pipeline.

Example fix

# before (produces the guard)
with zipfile.ZipFile(uploaded) as zf:
    zf.extractall(dest)  # unsafe if re-implemented

# after: pre-scan, then use safe_extract
import stat
with zipfile.ZipFile(uploaded) as zf:
    bad = [m.filename for m in zf.infolist() if stat.S_ISLNK(m.external_attr >> 16)]
    if bad:
        raise ValueError(f"quarantine: symlink entries {bad}")
    safe_extract(zf, dest)

import stat, zipfile

def has_symlink_entries(path: str) -> bool:
    with zipfile.ZipFile(path) as zf:
        return any(stat.S_ISLNK(m.external_attr >> 16) for m in zf.infolist())

from office.helpers import safe_extract
try:
    safe_extract(zf, dest)
except ValueError as e:
    if "symlink archive entry" in str(e):
        quarantine(path)  # untrusted input; do not repair
    else:
        raise

When it happens

Trigger: Unpacking a DOCX (or any zip passed to the unpack path) that contains an entry stored with S_IFLNK mode, e.g. 'word/document.xml -> /etc/passwd'. Common with deliberately crafted or fuzzed archives; standard Office files never contain symlink entries.

Common situations: Processing untrusted uploaded documents; archives rebuilt with tools that preserved symlinks; penetration-test payloads targeting naive ZipFile.extract() usage.

Related errors

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

AI-assisted analysis of anthropics/skills@f6656c1256 (2026-08-14). Data as JSON: /api/errors/eb727ad2e5336736. Report an issue: GitHub.