{"id":"CVE-2026-84382","aliases":["GHSA-8xx6-hgc6-gc2m","PYSEC-2026-3846"],"url":"https://o3.security/vulnerability/CVE-2026-84382","summary":"HTTPX2: Streaming response decompression does not bound peak memory (decompression amplification)","details":"### Summary\n\nWhen decoding a compressed response body (`gzip`, `deflate`, `br`, or `zstd`), HTTPX2 fully decompressed each network read before yielding content to the application. A small compressed input could therefore cause a large intermediate memory allocation, even when the application streamed the response to keep memory usage bounded.\n\n### Details\n\nHTTPX2's default transport reads the socket in pieces of up to 64 KiB. Before `2.12.0`, each piece was inflated completely into one intermediate allocation before any decompressed bytes were yielded.\n\nAt DEFLATE's maximum compression ratio of roughly 1032:1, a 64 KiB compressed chunk can expand to about 64 MiB in one allocation. Brotli and Zstandard responses can cause similarly large amplification. Streaming the response did not prevent these transient allocations.\n\n### Impact\n\nApplications that fetch resources from untrusted or attacker-influenced servers - such as webhook receivers, link unfurlers, crawlers, SSRF-reachable fetchers, and redirect followers - can experience memory pressure or out-of-memory termination when processing a malicious compressed response. No authentication or user interaction is required beyond issuing a request to the server.\n\n### Mitigation\n\nUpgrade to HTTPX2 `2.12.0` or later. Patched versions decompress responses incrementally with bounded intermediate buffers, including responses with multiple content encodings.","published":"2026-09-02T18:03:05.010Z","modified":"2026-09-11T03:30:38.632181488Z","cvss":{"score":7.5,"severity":"HIGH","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"},"epss":{"score":0.0035,"percentile":0.28498,"asOf":"2026-09-16"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"PyPI","name":"httpx2","fixedVersion":"2.12.0"}],"fix":{"url":"https://github.com/pydantic/httpx2/commit/4fd0c70a3f207c618b145934792f791bccfb39f8","label":"pydantic/httpx2@4fd0c70"},"references":[{"type":"WEB","url":"https://github.com/pydantic/httpx2/releases/tag/v2.12.0"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/84xxx/CVE-2026-84382.json"},{"type":"ADVISORY","url":"https://github.com/pydantic/httpx2/security/advisories/GHSA-8xx6-hgc6-gc2m"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-84382"},{"type":"FIX","url":"https://github.com/pydantic/httpx2/commit/4fd0c70a3f207c618b145934792f791bccfb39f8"},{"type":"FIX","url":"https://github.com/pydantic/httpx2/pull/1126"},{"type":"PACKAGE","url":"https://github.com/pydantic/httpx2"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-09-11T03:30:38.632181488Z"}}