CVE-2026-9375

urllib3 2.6.3 is vulnerable to a decompression bomb bypass in its streaming API when Brotli is enabled and preload_content is False. Three code paths in response.py bypass the max_length protection added in 2.6.0 to mitigate CVE-2025-66471: (1) negative max_length can result from buffer arithmeti...

Decompression bomb bypass via negative max_length in streaming API (incomplete fix for CVE-2025-66471)

Description The fix for CVE-2025-66471 in urllib3 2.6.0 added maxlength support to all decoders to prevent decompression bombs when using the streaming API. However, three independent code paths in response.py bypass this protection in urllib3 2.6.3 latest. Bypass 1 — Negative maxlength from buff...