Vulnerability-Lookup

GHSA-MWQ6-FG78-P6CQ

Vulnerability from github – Published: 2026-06-19 21:32 – Updated: 2026-06-19 21:32

Details

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.

Severity

7.5 (High)


                  
                    CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Show details on source website

JSON

To clipboard

{
  "affected": [],
  "aliases": [
    "CVE-2026-9375"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-400"
    ],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-06-19T19:16:36Z",
    "severity": "HIGH"
  },
  "details": "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.",
  "id": "GHSA-mwq6-fg78-p6cq",
  "modified": "2026-06-19T21:32:48Z",
  "published": "2026-06-19T21:32:48Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-9375"
    },
    {
      "type": "WEB",
      "url": "https://github.com/urllib3/urllib3/commit/2bdcc44d1e163fb5cc48a8662425e35e15adfe6a"
    },
    {
      "type": "WEB",
      "url": "https://huntr.com/bounties/ddd09eb9-b87d-4a43-84df-48837b1bbc23"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
      "type": "CVSS_V3"
    }
  ]
}

CVE-2026-9375 (GCVE-0-2026-9375)

Vulnerability from cvelistv5 – Published: 2026-06-19 18:45 – Updated: 2026-06-19 18:45

Title

Decompression Bomb Bypass via Negative max_length in Streaming API in urllib3

Summary

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.

Severity

7.5 (High)


                        
                          CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CWE

CWE-400 - Uncontrolled Resource Consumption

Assigner

@huntr_ai

References

2 references

URL	Tags
https://huntr.com/bounties/ddd09eb9-b87d-4a43-84d…
https://github.com/urllib3/urllib3/commit/2bdcc44…

Impacted products

1 product

Vendor	Product	Version
urllib3	urllib3/urllib3	Affected: unspecified , < 2.7.0 (custom)

Show details on NVD website

JSON

To clipboard

{
  "containers": {
    "cna": {
      "affected": [
        {
          "product": "urllib3/urllib3",
          "vendor": "urllib3",
          "versions": [
            {
              "lessThan": "2.7.0",
              "status": "affected",
              "version": "unspecified",
              "versionType": "custom"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "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."
        }
      ],
      "metrics": [
        {
          "cvssV3_0": {
            "attackComplexity": "LOW",
            "attackVector": "NETWORK",
            "availabilityImpact": "HIGH",
            "baseScore": 7.5,
            "baseSeverity": "HIGH",
            "confidentialityImpact": "NONE",
            "integrityImpact": "NONE",
            "privilegesRequired": "NONE",
            "scope": "UNCHANGED",
            "userInteraction": "NONE",
            "vectorString": "CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
            "version": "3.0"
          }
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-400",
              "description": "CWE-400 Uncontrolled Resource Consumption",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-06-19T18:45:10.409Z",
        "orgId": "c09c270a-b464-47c1-9133-acb35b22c19a",
        "shortName": "@huntr_ai"
      },
      "references": [
        {
          "url": "https://huntr.com/bounties/ddd09eb9-b87d-4a43-84df-48837b1bbc23"
        },
        {
          "url": "https://github.com/urllib3/urllib3/commit/2bdcc44d1e163fb5cc48a8662425e35e15adfe6a"
        }
      ],
      "source": {
        "advisory": "ddd09eb9-b87d-4a43-84df-48837b1bbc23",
        "discovery": "EXTERNAL"
      },
      "title": "Decompression Bomb Bypass via Negative max_length in Streaming API in urllib3"
    }
  },
  "cveMetadata": {
    "assignerOrgId": "c09c270a-b464-47c1-9133-acb35b22c19a",
    "assignerShortName": "@huntr_ai",
    "cveId": "CVE-2026-9375",
    "datePublished": "2026-06-19T18:45:10.409Z",
    "dateReserved": "2026-05-23T14:33:21.716Z",
    "dateUpdated": "2026-06-19T18:45:10.409Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

Action not permitted

GHSA-MWQ6-FG78-P6CQ

CVE-2026-9375 (GCVE-0-2026-9375)

Tags

Sightings

Nomenclature