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CVE Record

CVE-2025-0938: URL parser allowed square brackets in domain names

The Python standard library functions `urllib.parse.urlsplit` and `urlparse` accepted domain names that included square brackets which isn't valid according to RFC 3986. Square brackets are only meant to be used as delimiters for specifying IPv6 and IPvFuture hosts in URLs. This could result in differential parsing across the Python URL parser and other specification-compliant URL parsers.

MediumCVSS 6.3Not KEV-listedUpdated
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Security readout for executives and security teams

Plain-English summary

Python’s built-in URL parser accepted domain names containing square brackets, which standards reserve for IPv6-style hosts. If an application uses Python parsing to make trust decisions, another compliant parser may interpret the same URL differently. This can create security logic bypasses in URL validation, redirects, or filtering.

Executive priority

Treat as a moderate-priority patch and code-review item. It is not documented as actively exploited, but it can affect trust boundaries in URL-heavy applications. Prioritize externally reachable services and products that validate third-party URLs.

Technical view

CVE-2025-0938 affects CPython urllib.parse.urlsplit and urlparse. The parser accepted invalid bracketed domain names, creating differential parsing versus RFC 3986-compliant parsers. The CVE is CWE-20 with CVSS 4.0 score 6.3. Impact is limited integrity impact, network reachable, high complexity, and requires specific attack conditions.

Likely exposure

Exposure is most likely in Python applications that parse user-supplied URLs for allowlists, blocklists, redirects, SSRF controls, webhook validation, or domain trust checks. Systems using only patched Python runtimes or not using urllib.parse for security decisions are less exposed.

Exploitation context

The source bundle does not show CISA KEV listing or cited active exploitation. Practical exploitation depends on an application making security decisions from Python’s parsed hostname while another component interprets the URL differently.

Researcher notes

The main security issue is parser differential behavior, not memory corruption or remote code execution. Evidence includes Python issue tracking, a pull request, multiple patch commits, and a Python security announcement. Fixed version details should be taken from vendor or distribution advisories.

Mitigation direction

  • Apply CPython security updates or vendor backports that include the linked urllib.parse patches.
  • Check Python Software Foundation, OS distribution, and appliance vendor advisories for fixed package versions.
  • Prioritize internet-facing services that process untrusted URLs or enforce domain-based access rules.
  • Review code that relies on urlsplit or urlparse for security-sensitive hostname decisions.

Validation and detection

  • Inventory CPython versions across servers, containers, developer images, and appliances.
  • Identify applications using urllib.parse.urlsplit or urlparse on untrusted input.
  • Confirm installed Python packages include vendor patches or distribution backports for CVE-2025-0938.
  • Test URL validation logic for consistent rejection of invalid bracketed domain names.
  • Review downstream advisories, including Debian and NetApp, where applicable.
Prepared
Confidence
high
Sources
8

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

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ATT&CK lookup starting points

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CVE-2025-0938 mapping review

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Vulnerability profileCVE Program record
Severity
Medium
CVSS
6.3 (4.0)
Known Exploited
No
Published

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

Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

1CVSS vectors
3Timeline events
2ADP providers
12Source links

SSVC decision data

CISA-ADPCISA Coordinator
Timestamp
Version
2.0.3
Exploitation: noneAutomatable: noTechnical Impact: partial

CVSS vector scores

1 official score

We collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.

ScoreVersionSeverityVectorExploitImpactSource
6.3CVSS 4.0MediumCVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:L/SA:N——PSF

Vulnerability scoring details

Base CVSS 4.0 score

6.3Medium
CVSS 4.0 vector shape for CVE-2025-0938Attack VectorAttack ComplexityAttack RequirementsPrivileges RequiredUser InteractionVS ConfidentialityVS IntegrityVS AvailabilitySS ConfidentialitySS IntegritySS Availability

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

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Attack Requirements
NonePresent
Privileges Required
NoneLowHigh
User Interaction
NonePassiveActive
VS Confidentiality
HighLowNone
VS Integrity
HighLowNone
VS Availability
HighLowNone
SS Confidentiality
HighLowNone
SS Integrity
HighLowNone
SS Availability
HighLowNone

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  2. CVE publishedCVE Program

    The CVE record was published.

  3. CVE updatedCVE Program

    The CVE record metadata indicates this as the latest update time.

ADP provider summaries

CISA-ADPCISA ADP Vulnrichment
other:ssvc
CVECVE Program Container

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
Python Software FoundationCPython0, 3.10.0, 3.11.0, 3.12.0, 3.13.0, 3.14.0a1unaffected
Weakness

CWE details

CWE-20

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.