CVE-2025-66418VulnerabilityPublished 26 Jan 2026Updated 8 Oct 2026

Red Hat Security Advisory: python3.11-urllib3 security update

Affects Red HatSource GCVE Database

Mentioned vulnerabilities

Not known to be exploited.

Data as of 25 Oct 2026, 19:02 UTC

Severity

High

Rated by Threat Radar · No CVSS score from NVD or the CNA

EPSS: 0.6% chance of exploitation in 30 days – higher than 52% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.

Exploitation evidence

Disclosed: evidence found.
CVE published 26 Jan 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 2026-10-25.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Affected software

Product	Affected	Fixed in
Red Hat Product Security Red Hat	Affected Red Hat Red Hat Enterprise Linux Red Hat Enterprise Linux AppStream (v. 8) src python3.11-urllib3-0:1.26.12-6.el8_10.src	Fixed in–

AI-suggested

Red Hat has released updated python3.11-urllib3 packages that address these vulnerabilities. Users should apply the security update for python3.11-urllib3 as provided in Red Hat Enterprise Linux 8 and Extended Life Cycle 8.10. Details and instructions for applying the update are available at https://access.redhat.com/articles/11258. No additional mitigation steps are indicated beyond applying the official update.

Description

Python is an interpreted, interactive, object-oriented programming language, which includes modules, classes, exceptions, very high level dynamic data types and dynamic typing. Python supports interfaces to many system calls and libraries, as well as to various windowing systems. Security Fix(es): * urllib3: urllib3: Unbounded decompression chain leads to resource exhaustion (CVE-2025-66418) * urllib3: urllib3 Streaming API improperly handles highly compressed data (CVE-2025-66471) * urllib3: urllib3 vulnerable to decompression-bomb safeguard bypass when following HTTP redirects (streaming API) (CVE-2026-21441) For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

Impact

The vulnerabilities can lead to resource exhaustion or denial of service conditions when processing specially crafted compressed data streams using urllib3's streaming API. This can affect systems running vulnerable versions of python3.11-urllib3 on Red Hat Enterprise Linux 8, potentially impacting availability of affected services.

Summary

This advisory addresses three security issues in the urllib3 library used by python3.11 on Red Hat Enterprise Linux 8. CVE-2025-66418 involves an unbounded decompression chain that can cause resource exhaustion. CVE-2025-66471 concerns improper handling of highly compressed data by the urllib3 streaming API. CVE-2026-21441 describes a vulnerability where the decompression-bomb safeguard can be bypassed when following HTTP redirects in the streaming API. These issues could lead to denial of service or resource exhaustion conditions. Red Hat has released updated python3.11-urllib3 packages to fix these vulnerabilities.

CWE-770Allocation of Resources Without Limits or Throttling (opens in a new tab)
Base weaknessLikelihood of exploit: HighCWE Top 25 (2025): #25
The product allocates a reusable resource or group of resources on behalf of an actor without imposing any intended restrictions on the size or number of resources that can be allocated.
Requirements
Clearly specify the minimum and maximum expectations for capabilities, and dictate which behaviors are acceptable when resource allocation reaches limits.
Architecture and Design
Limit the amount of resources that are accessible to unprivileged users. Set per-user limits for resources. Allow the system administrator to define these limits. Be careful to avoid CWE-410.
Architecture and Design
Design throttling mechanisms into the system architecture. The best protection is to limit the amount of resources that an unauthorized user can cause to be expended.
OWASP Cheat Sheets
Abuse Case (opens in a new tab)
OWASP ASVS 4.0.3
V8.1.4 (opens in a new tab)
V13.4.1 (opens in a new tab)
V11.1.4 (opens in a new tab)
Attack patterns
XML Ping of the Death (opens in a new tab)
Exponential Data Expansion (opens in a new tab)
Serialized Data Parameter Blowup (opens in a new tab)
Serialized Data with Nested Payloads (opens in a new tab)
Oversized Serialized Data Payloads (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).
CWE-409Improper Handling of Highly Compressed Data (Data Amplification) (opens in a new tab)
Base weakness
The product does not handle or incorrectly handles a compressed input with a very high compression ratio that produces a large output.
OWASP Cheat Sheets
File Upload (opens in a new tab)
OWASP ASVS 4.0.3
V12.1.2 (opens in a new tab)
V12.1.1 (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 10 Aug 2026, 17:58 UTC

WeaknessesCWE-770, CWE-409

Technical details

References

Community reviews

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