Vulnerability-Lookup

CVE-2026-97689 (GCVE-0-2026-97689)

Vulnerability from cvelistv5 – Published: 2026-09-29 15:36 – Updated: 2026-09-29 16:23

Title

urllib3: HTTPResponse.stream()/read_chunked() buffers an unbounded chunk-size line into memory

Summary

urllib3 is an HTTP client library for Python. From 1.10.3 until 2.8.0, the HTTPResponse.read_chunked and HTTPResponse.stream methods can allocate unbounded memory because the streaming chunk parser buffers the chunk-size field until newline or EOF without a length bound. The trigger is that a malicious server returns Transfer-Encoding: chunked followed by a very long run of bytes without a newline. The attack mechanism is that a malicious HTTP server sends a very long unterminated chunk-size line. The impact is that unbounded memory allocation can exhaust the client process. This issue is fixed in version 2.8.0.

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

SSVC

Exploitation: none Automatable: no Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-09-29 16:21 UTC

CWE

CWE-770 - Allocation of Resources Without Limits or Throttling

Assigner

GitHub_M mitre root Scorecard

References

3 references

URL	Tags
https://github.com/urllib3/urllib3/security/advis…	x_refsource_CONFIRM
https://github.com/urllib3/urllib3/commit/cd770b0…	x_refsource_MISC
https://github.com/urllib3/urllib3/releases/tag/2.8.0	x_refsource_MISC

Impacted products

1 product

Vendor	Product	Version	CPE status
urllib3	urllib3	Affected: >= 1.10.3, < 2.8.0	guessed

Show details on NVD website

JSON

To clipboard

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FKIE_CVE-2026-97689

Vulnerability from fkie_nvd - Published: 2026-09-29 16:17 - Updated: 2026-09-29 17:17

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

Summary

References

	URL	Tags
	security-advisories@github.com	https://github.com/urllib3/urllib3/commit/cd770b059b543be29298ea5c52afb0b1b090f5ed
	security-advisories@github.com	https://github.com/urllib3/urllib3/releases/tag/2.8.0
	security-advisories@github.com	https://github.com/urllib3/urllib3/security/advisories/GHSA-vxq7-64xx-v4gw

Impacted products

	Vendor	Product	Version

JSON

To clipboard

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GHSA-VXQ7-64XX-V4GW

Vulnerability from github – Published: 2026-09-30 14:46 – Updated: 2026-09-30 14:46

Summary

urllib3: HTTPResponse.stream()/read_chunked() buffers an unbounded chunk-size line into memory

Details

Impact

urllib3's streaming API is designed for efficiently handling large HTTP responses by reading the content in chunks, rather than loading the entire response body into memory at once. When decoding a chunked-transfer-encoded response, this API reads each chunk's size field by buffering until it sees \n or EOF.

A malicious HTTP server can return Transfer-Encoding: chunked and then send a very long run of bytes without any newline, causing the streaming client to buffer that entire run before urllib3 can reject the chunk size as invalid and allocate more memory than intended.

To fix the issue, we'll reject chunk-size fields larger than 65536 bytes, as already done in the non-streaming case, which is currently handled by the Python standard library. Note that this only applies to reading the chunk-size field, not the chunk data, which is already handled correctly. Thus, there shouldn't be any impact for non-malicious servers.

Affected usages

Applications and libraries using urllib3 versions earlier than 2.8.0 may be affected when streaming a chunked response from untrusted sources. Specifically, this affects the read_chunked() and stream() methods of the HTTPResponse object.

This also affects requests streaming API, which uses urllib3 under the hood.

Remediation

Upgrade to urllib3 version 2.8.0 or later, where chunk-size fields larger than 65536 will be rejected. If upgrading is not immediately possible, consider reading the response at once using the read() method.

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

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{
  "affected": [
    {
      "package": {
        "ecosystem": "PyPI",
        "name": "urllib3"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "1.10.3"
            },
            {
              "fixed": "2.8.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-97689"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-770"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-09-30T14:46:18Z",
    "nvd_published_at": "2026-09-29T16:17:18Z",
    "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 efficiently handling large HTTP responses by reading the content in chunks, rather than loading the entire response body into memory at once. When decoding a [chunked-transfer-encoded response](https://httpwg.org/specs/rfc9112.html#chunked.encoding), this API reads each chunk\u0027s size field by buffering until it sees `\\n` or EOF.\n\nA malicious HTTP server can return `Transfer-Encoding: chunked` and then send a very long run of bytes without any newline, causing the streaming client to buffer that entire run before urllib3 can reject the chunk size as invalid and allocate more memory than intended.\n\nTo fix the issue, we\u0027ll reject chunk-size fields larger than 65536 bytes, as already done in the non-streaming case, which is currently handled by the Python standard library. Note that this only applies to reading the chunk-size field, not the chunk data, which is already handled correctly. Thus, there shouldn\u0027t be any impact for non-malicious servers.\n\n## Affected usages\n\nApplications and libraries using urllib3 versions earlier than 2.8.0 may be affected when streaming a chunked response from untrusted sources. Specifically, this affects the [read_chunked()](https://urllib3.readthedocs.io/en/stable/reference/urllib3.response.html#urllib3.response.BaseHTTPResponse.read_chunked) and [stream()](https://urllib3.readthedocs.io/en/stable/reference/urllib3.response.html#urllib3.response.BaseHTTPResponse.stream) methods of the HTTPResponse object.\n\nThis also affects requests streaming API, which uses urllib3 under the hood.\n\n## Remediation\n\nUpgrade to urllib3 version 2.8.0 or later, where chunk-size fields larger than 65536 will be rejected. If upgrading is not immediately possible, consider reading the response at once using the [read()](https://urllib3.readthedocs.io/en/stable/reference/urllib3.response.html#urllib3.response.BaseHTTPResponse.read) method.",
  "id": "GHSA-vxq7-64xx-v4gw",
  "modified": "2026-09-30T14:46:18Z",
  "published": "2026-09-30T14:46:18Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/urllib3/urllib3/security/advisories/GHSA-vxq7-64xx-v4gw"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-97689"
    },
    {
      "type": "WEB",
      "url": "https://github.com/urllib3/urllib3/commit/cd770b059b543be29298ea5c52afb0b1b090f5ed"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/urllib3/urllib3"
    },
    {
      "type": "WEB",
      "url": "https://github.com/urllib3/urllib3/releases/tag/2.8.0"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "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: HTTPResponse.stream()/read_chunked() buffers an unbounded chunk-size line into memory"
}

RHSA-2026:69612

Vulnerability from csaf_redhat - Published: 2026-09-21 19:00 - Updated: 2026-09-30 10:23

Summary

Red Hat Security Advisory: Red Hat Hardened Images RPMs bug fix and enhancement update

Severity

Important

Scope

3 vulnerabilities in this advisory, including CVE-2026-97689.

CVE-2026-97689

A flaw was found in urllib3. This flaw allows a Denial of Service (DoS) through unbounded memory allocation when parsing chunk-encoded responses. A malicious server can send an excessively long chunk-size line without a newline, exhausting client memory and terminating the application.

7.5 (High)


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

Fixed: 11 products

https://access.redhat.com/errata/RHSA-2026:69612

Open the full advisory

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.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.

Related by attack behaviour

Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.

Action not permitted

CVE-2026-97689 (GCVE-0-2026-97689)

FKIE_CVE-2026-97689

GHSA-VXQ7-64XX-V4GW

Impact

Affected usages

Remediation

RHSA-2026:69612

Tags

Sightings

Nomenclature

Related by attack behaviour