CVE-2026-9375 | Decompression Bomb Bypass via Negative max_length in Streaming API in urllib3

urllib3 version 2.6.3 is vulnerable to a decompression bomb bypass in its streaming API (`preload_content=False`) when using Brotli support. The issue arises due to three independent code paths in `response.py` that bypass the `max_length` protection introduced in version 2.6.0 to mitigate CVE-2025-66471. Specifically, negative `max_length` values can be produced due to buffer arithmetic in `read()`, `flush_decoder` unconditionally overrides `max_length` to `-1`, and `_flush_decoder()` passes no limit at all, defaulting to unlimited decompression. This allows a malicious HTTP server to trigger an out-of-memory (OOM) condition by decompressing large payloads into memory, leading to a denial of service (DoS). The vulnerability affects urllib3 2.6.3 and Brotli 1.2.0 and impacts applications and libraries using `requests` or `urllib3` to stream content from untrusted sources.

Published: 2026-06-19 Last update: 2026-06-22 Assigner: [email protected] Source: [email protected]
NVD Status：Deferred，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2026-9375 is rated Low Risk (37.7/100): CVSS High severity, with low exploitation likelihood (EPSS 0.30%). Monitor for updates and reassess as exploit intelligence or EPSS changes.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2026-9375

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-23 — 0.30% —

Full EPSS history (1 record total)

Common vulnerability scoring system (CVSS) metrics for CVE-2026-9375

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
7.5 3.0 HIGH
CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 3.9 3.6 [email protected]

Weakness enumeration for CVE-2026-9375

GitHub Security Advisory for CVE-2026-9375

GHSA-mwq6-fg78-p6cq · Severity: high — urllib3 version 2.6.3 is vulnerable to a decompression bomb bypass in its streaming API (...

OS Trackers for CVE-2026-9375

vendor priority summary link
debian not yet assigned CVE-2026-9375 not yet assigned priority: Debian including 1 source packages (python-urllib3), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): open 4, resolved 1. https://security-tracker.debian.org/tracker/CVE-2026-9375
suse medium CVE-2026-9375 severity moderate: SUSE including 8 source package names (python-urllib3, python-urllib3_1, …), 61 product×package rows across 25 product lines (SUSE Linux Enterprise High Performance Computing 15 SP4-LTSS, SUSE Linux Enterprise High Performance Computing 15 SP5-LTSS, … (25 product lines)): Known Not Affected 61. https://www.suse.com/security/cve/CVE-2026-9375/
ubuntu medium CVE-2026-9375 medium priority: Ubuntu including 2 source packages (python-pip, python-urllib3), 17 status rows across 9 suites (bionic, focal, jammy, noble, questing, resolute, trusty, upstream, xenial): needs-triage 17. https://ubuntu.com/security/CVE-2026-9375

Affected software / configurations for CVE-2026-9375

Vendor Product Version Raw CPE
No affected products in dataset.

References for CVE-2026-9375

cvelogic Threat Intelligence