Vulnerability-Lookup

PYSEC-2026-142

Vulnerability from pysec - Published: 2026-05-13 16:16 - Updated: 2026-05-20 09:19

Details

urllib3 is an HTTP client library for Python. From 2.6.0 to before 2.7.0, urllib3 could decompress the whole response instead of the requested portion (1) during the second HTTPResponse.read(amt=N) call when the response was decompressed using the official Brotli library or (2) when HTTPResponse.drain_conn() was called after the response had been read and decompressed partially (compression algorithm did not matter here). These issues could cause urllib3 to fully decode a small amount of highly compressed data in a single operation. This could result in excessive resource consumption (high CPU usage and massive memory allocation for the decompressed data) on the client side. This vulnerability is fixed in 2.7.0.

Severity ?

7.5 (High)


                  
                    CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Impacted products

Name	purl
urllib3	pkg:pypi/urllib3

Aliases

JSON

To clipboard

{
  "affected": [
    {
      "package": {
        "ecosystem": "PyPI",
        "name": "urllib3",
        "purl": "pkg:pypi/urllib3"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "2.6.0"
            },
            {
              "fixed": "2.7.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "2.6.0",
        "2.6.1",
        "2.6.2",
        "2.6.3"
      ]
    }
  ],
  "aliases": [
    "CVE-2026-44432",
    "GHSA-mf9v-mfxr-j63j"
  ],
  "details": "urllib3 is an HTTP client library for Python. From 2.6.0 to before 2.7.0, urllib3 could decompress the whole response instead of the requested portion (1) during the second HTTPResponse.read(amt=N) call when the response was decompressed using the official Brotli library or (2) when HTTPResponse.drain_conn() was called after the response had been read and decompressed partially (compression algorithm did not matter here). These issues could cause urllib3 to fully decode a small amount of highly compressed data in a single operation. This could result in excessive resource consumption (high CPU usage and massive memory allocation for the decompressed data) on the client side. This vulnerability is fixed in 2.7.0.",
  "id": "PYSEC-2026-142",
  "modified": "2026-05-20T09:19:21.038869Z",
  "published": "2026-05-13T16:16:57.303Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://github.com/urllib3/urllib3/security/advisories/GHSA-mf9v-mfxr-j63j"
    }
  ],
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
      "type": "CVSS_V3"
    }
  ]
}

CVE-2026-44432 (GCVE-0-2026-44432)

Vulnerability from cvelistv5 – Published: 2026-05-13 15:17 – Updated: 2026-05-15 18:25

Title

urllib3: Decompression-bomb safeguards bypassed in parts of the streaming API

Summary

Severity ?

8.9 (High)


                        
                          CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:H

CWE

CWE-409 - Improper Handling of Highly Compressed Data (Data Amplification)

Assigner

GitHub_M

References

1 reference

URL	Tags
https://github.com/urllib3/urllib3/security/advis…	x_refsource_CONFIRM

Impacted products

1 product

Vendor	Product	Version
urllib3	urllib3	Affected: >= 2.6.0, < 2.7.0

Show details on NVD website

JSON

To clipboard

{
  "containers": {
    "adp": [
      {
        "metrics": [
          {
            "other": {
              "content": {
                "id": "CVE-2026-44432",
                "options": [
                  {
                    "Exploitation": "none"
                  },
                  {
                    "Automatable": "no"
                  },
                  {
                    "Technical Impact": "partial"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-05-15T18:17:39.119999Z",
                "version": "2.0.3"
              },
              "type": "ssvc"
            }
          }
        ],
        "providerMetadata": {
          "dateUpdated": "2026-05-15T18:25:06.331Z",
          "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "shortName": "CISA-ADP"
        },
        "title": "CISA ADP Vulnrichment"
      }
    ],
    "cna": {
      "affected": [
        {
          "product": "urllib3",
          "vendor": "urllib3",
          "versions": [
            {
              "status": "affected",
              "version": "\u003e= 2.6.0, \u003c 2.7.0"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "urllib3 is an HTTP client library for Python. From 2.6.0 to before 2.7.0, urllib3 could decompress the whole response instead of the requested portion (1) during the second HTTPResponse.read(amt=N) call when the response was decompressed using the official Brotli library or (2) when HTTPResponse.drain_conn() was called after the response had been read and decompressed partially (compression algorithm did not matter here). These issues could cause urllib3 to fully decode a small amount of highly compressed data in a single operation. This could result in excessive resource consumption (high CPU usage and massive memory allocation for the decompressed data) on the client side. This vulnerability is fixed in 2.7.0."
        }
      ],
      "metrics": [
        {
          "cvssV4_0": {
            "attackComplexity": "LOW",
            "attackRequirements": "PRESENT",
            "attackVector": "NETWORK",
            "baseScore": 8.9,
            "baseSeverity": "HIGH",
            "privilegesRequired": "NONE",
            "subAvailabilityImpact": "HIGH",
            "subConfidentialityImpact": "NONE",
            "subIntegrityImpact": "NONE",
            "userInteraction": "NONE",
            "vectorString": "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:H",
            "version": "4.0",
            "vulnAvailabilityImpact": "HIGH",
            "vulnConfidentialityImpact": "NONE",
            "vulnIntegrityImpact": "NONE"
          }
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-409",
              "description": "CWE-409: Improper Handling of Highly Compressed Data (Data Amplification)",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-05-13T15:17:12.611Z",
        "orgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
        "shortName": "GitHub_M"
      },
      "references": [
        {
          "name": "https://github.com/urllib3/urllib3/security/advisories/GHSA-mf9v-mfxr-j63j",
          "tags": [
            "x_refsource_CONFIRM"
          ],
          "url": "https://github.com/urllib3/urllib3/security/advisories/GHSA-mf9v-mfxr-j63j"
        }
      ],
      "source": {
        "advisory": "GHSA-mf9v-mfxr-j63j",
        "discovery": "UNKNOWN"
      },
      "title": "urllib3: Decompression-bomb safeguards bypassed in parts of the streaming API"
    }
  },
  "cveMetadata": {
    "assignerOrgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
    "assignerShortName": "GitHub_M",
    "cveId": "CVE-2026-44432",
    "datePublished": "2026-05-13T15:17:12.611Z",
    "dateReserved": "2026-05-06T14:40:00.954Z",
    "dateUpdated": "2026-05-15T18:25:06.331Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}

GHSA-MF9V-MFXR-J63J

Vulnerability from github – Published: 2026-05-11 14:51 – Updated: 2026-05-14 20:35

Summary

urllib3: Decompression-bomb safeguards bypassed in parts of the streaming API

Details

Impact

urllib3's streaming API is designed for the efficient handling of large HTTP responses by reading the content in chunks, rather than loading the entire response body into memory at once.

urllib3 can perform decompression based on the HTTP Content-Encoding header (e.g., gzip, deflate, br, or zstd). When using the streaming API since version 2.6.0, the library decompresses only the necessary bytes, enabling partial content consumption.

However, urllib3 before version 2.7.0 could still decompress the whole response instead of the requested portion in two cases: 1. During the second HTTPResponse.read(amt=N) call when the response was decompressed using the official Brotli library. 2. When HTTPResponse.drain_conn() was called after the response had been read and decompressed partially (compression algorithm did not matter here).

These issues could cause urllib3 to fully decode a small amount of highly compressed data in a single operation. This could result in excessive resource consumption (high CPU usage and massive memory allocation for the decompressed data; CWE-409) on the client side.

Affected usages

Applications and libraries using urllib3 versions earlier than 2.7.0 may be affected when streaming compressed responses from untrusted sources in either of these cases, unless decompression is explicitly disabled:

A response encoded with br is read incrementally with at least two HTTPResponse.read(amt=N) or HTTPResponse.stream(amt=N) calls while using the official Brotli library.
HTTPResponse.drain_conn() is called after response decompression has already started.

Remediation

Upgrade to at least urllib3 version 2.7.0 in which the library: 1. Is more efficient for reads with Brotli. 2. Always skips decompression for HTTPResponse.drain_conn().

If upgrading is not immediately possible, the following workarounds may reduce exposure in specific cases: 1. For the Brotli-specific issue only, switch from brotli to brotlicffi until you can upgrade urllib3; the official Brotli package is affected because of https://github.com/google/brotli/issues/1396. 2. If your code explicitly calls HTTPResponse.drain_conn(), call HTTPResponse.close() instead when connection reuse is not important.

Credits

The Brotli-specific issue was reported by @kimkou2024. HTTPResponse.drain_conn() inefficiency was reported by @Cycloctane.

Severity ?

7.5 (High)


                  
                    CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

8.9 (High)


                  
                    CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:H

Show details on source website

JSON

To clipboard

{
  "affected": [
    {
      "package": {
        "ecosystem": "PyPI",
        "name": "urllib3"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "2.6.0"
            },
            {
              "fixed": "2.7.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-44432"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-409"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-05-11T14:51:45Z",
    "nvd_published_at": "2026-05-13T16:16:57Z",
    "severity": "HIGH"
  },
  "details": "### Impact\n\nurllib3\u0027s [streaming API](https://urllib3.readthedocs.io/en/2.7.0/advanced-usage.html#streaming-and-i-o) is designed for the efficient handling of large HTTP responses by reading the content in chunks, rather than loading the entire response body into memory at once.\n\nurllib3 can perform decompression based on the HTTP `Content-Encoding` header (e.g., `gzip`, `deflate`, `br`, or `zstd`). When using the streaming API since version 2.6.0, the library decompresses only the necessary bytes, enabling partial content consumption.\n\nHowever, urllib3 before version 2.7.0 could still decompress the whole response instead of the requested portion in two cases:\n1. During the second `HTTPResponse.read(amt=N)` call when the response was decompressed using the official [Brotli](https://pypi.org/project/brotli/) library.\n2. When `HTTPResponse.drain_conn()` was called after the response had been read and decompressed partially (compression algorithm did not matter here).\n\nThese issues could cause urllib3 to fully decode a small amount of highly compressed data in a single operation. This could result in excessive resource consumption (high CPU usage and massive memory allocation for the decompressed data; CWE-409) on the client side.\n\n\n### Affected usages\n\nApplications and libraries using urllib3 versions earlier than 2.7.0 may be affected when streaming compressed responses from untrusted sources in either of these cases, unless decompression is explicitly disabled:\n\n1. A response encoded with `br` is read incrementally with at least two `HTTPResponse.read(amt=N)` or `HTTPResponse.stream(amt=N)` calls while using the official [Brotli](https://pypi.org/project/brotli/) library.\n2. `HTTPResponse.drain_conn()` is called after response decompression has already started.\n\n\n### Remediation\n\nUpgrade to at least urllib3 version 2.7.0 in which the library:\n1. Is more efficient for reads with Brotli.\n2. Always skips decompression for `HTTPResponse.drain_conn()`.\n\nIf upgrading is not immediately possible, the following workarounds may reduce exposure in specific cases:\n1. For the Brotli-specific issue only, switch from [brotli](https://pypi.org/project/brotli/) to [brotlicffi](https://pypi.org/project/brotlicffi/) until you can upgrade urllib3; the official Brotli package is affected because of https://github.com/google/brotli/issues/1396.\n2. If your code explicitly calls `HTTPResponse.drain_conn()`, call `HTTPResponse.close()` instead when connection reuse is not important.\n\n\n### Credits\n\nThe Brotli-specific issue was reported by @kimkou2024.\n`HTTPResponse.drain_conn()` inefficiency was reported by @Cycloctane.",
  "id": "GHSA-mf9v-mfxr-j63j",
  "modified": "2026-05-14T20:35:53Z",
  "published": "2026-05-11T14:51:45Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/urllib3/urllib3/security/advisories/GHSA-mf9v-mfxr-j63j"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-44432"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/urllib3/urllib3"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
      "type": "CVSS_V3"
    },
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:H",
      "type": "CVSS_V4"
    }
  ],
  "summary": "urllib3: Decompression-bomb safeguards bypassed in parts of the streaming API"
}

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

PYSEC-2026-142

CVE-2026-44432 (GCVE-0-2026-44432)

GHSA-MF9V-MFXR-J63J

Impact

Affected usages

Remediation

Credits

Tags

Sightings

Nomenclature