CVE-2025-66418VulnerabilityPublished 28 Jan 2026Updated 29 Oct 2026

Red Hat Security Advisory: RHUI 4.11.3 security update - python-urllib3

Affects Red Hat RHUI 4.11.3Source GCVE Database

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Mentioned vulnerabilities

Not known to be exploited.

Data as of 29 Oct 2026, 09:13 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 28 Jan 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: 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 29 Oct 2026.

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.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity 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 Update Infrastructure RHUI 4 for RHEL 8 src python-urllib3-0:2.6.3-1.el8ui.src	Fixed in–

Description

Red Hat Update Infrastructure (RHUI) provides a highly scalable and redundant framework for managing repositories and content. It also allows cloud providers to deliver content and updates to Red Hat Enterprise Linux (RHEL) instances. Security Fixes: Python-urllib3: Unbounded decompression chain leads to resource exhaustion (CVE-2025-66418) Python-urllib3: urllib3 vulnerable to decompression-bomb safeguard bypass when following HTTP redirects (CVE-2026-21441) Python-urllib3: urllib3 Streaming API improperly handles highly compressed data (CVE-2025-66471) This update addresses several vulnerabilities within the urllib3 library pertaining to the handling of compressed content (e.g., gzip, deflate, br, or zstd). A remote attacker could potentially provide specially crafted content that, when processed, leads to excessive CPU utilization and significant memory allocation during decompression, potentially resulting in a denial-of-service (DoS) condition. Deployment Notes: * RHUA nodes: The updated python3-urllib3 package provided in this errata is intended specifically for Red Hat Update Appliance (RHUA) nodes. * CDS nodes: Content Delivery Server (CDS) nodes should receive the corresponding update directly from the standard Red Hat Enterprise Linux (RHEL) distribution channels. Impact Assessment: Under standard operating conditions, a properly secured RHUI environment is not expected to be impacted by these vulnerabilities, as the RHUA typically communicates only with trusted endpoints. However, as a matter of security best practice, all RHUI administrators are strongly advised to apply this update to mitigate potential risks.

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

Community reviews

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Exploitation evidence

What to do

Affected software

Description

WeaknessesCWE-770, CWE-409

Technical details

References

Community reviews

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