CVE-2026-97689

highpriority · track · 30EPSS 0.003 · 26 %ileDEFRUS
grimoire priorityP2 · Scheduled
Exploitable?
—
no known exploitation
Likely / severe?
0.34% (26th) EPSS
CVSS 7.5 · high
Is it mine?
8 products
Check your exposure
Who says so?
4 sources
osv · cert_bund · nvd · certfr

EPSS · scored 2026-10-22

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.

01

cvss

Technical severity, 0–10. One row per scoring source.

8.9
010

base score 0–10 · higher = more severe · hover a vector to decode⚠ sources disagree · medium–high · 6.3–8.9

v3.17.5highCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:Hprimary · NVD / NIST USexploitability 3.9 · impact 3.6
v4.08.9highCVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:H/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:Xsecondary · security-advisories@github.com
v4.06.3mediumCVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:H/E:U/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:Xsecondary · CVSS-BT (t0sche)
02

ssvc

A stakeholder decision — act, attend, or track — from exploitation and impact.

Trackcoordinatorcisa_ssvcUS
03

weaknesses

The CWE weakness classes this flaw belongs to.

04

affected products (8)

Products and version ranges known to be affected.

05

advisories (5)

Vendor and ecosystem advisories describing this.

  • WID-SEC-W-2026-4024Red Hat Quay und Enterprise Linux (pypdf, urllib3, URI): Mehrere SchwachstellenDeutsch2026-10-18csaf · cert_bundDE

    Ein entfernter, anonymer Angreifer kann mehrere Schwachstellen in Red Hat Quay und Red Hat Enterprise Linux ausnutzen, um einen Denial of Service Angriff durchzuführen oder Sicherheitsmaßnahmen zu umgehen.

  • GHSA-vxq7-64xx-v4gwurllib3: HTTPResponse.stream()/read_chunked() buffers an unbounded chunk-size line into memory2026-09-30ghsa · osvUS

    ## Impact urllib3's [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'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()](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. 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()](https://urllib3.readthedocs.io/en/stable/reference/urllib3.response.html#urllib3.response.BaseHTTPResponse.read) method.

  • CERTFR-2026-AVI-1376Multiples vulnérabilités dans le noyau Linux d'UbuntuFrançais2026-10-23vendor · certfrFR
  • CERTFR-2026-AVI-1378Multiples vulnérabilités dans les produits IBMFrançais2026-10-23vendor · certfrFR
  • PYSEC-2026-4177urllib3: HTTPResponse.stream()/read_chunked() buffers an unbounded chunk-size line into memory2026-10-01vendor · osvUS

    ## Impact urllib3's [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'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()](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. 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()](https://urllib3.readthedocs.io/en/stable/reference/urllib3.response.html#urllib3.response.BaseHTTPResponse.read) method.

06

also known as (2)

Other names and identifiers for this entity.

07

sources

Which sources assert this record, and when.

published 2026-09-29modified 2026-10-13
08

references (3) nvd

External citations — patches, advisories, analysis.

scry

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