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CVE Record

CVE-2026-4786: Incomplete mitigation of CVE-2026-4519, %action expansion for command injection to webbrowser.open()

Mitgation of CVE-2026-4519 was incomplete. If the URL contained "%action" the mitigation could be bypassed for certain browser types the "webbrowser.open()" API could have commands injected into the underlying shell. See CVE-2026-4519 for details.

HighCVSS 7.1Not KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

CVE-2026-4786 is a high-severity CPython issue where an incomplete fix left some webbrowser.open() calls vulnerable to command injection when a URL contains %action. Business risk depends on whether applications pass attacker-controlled URLs into that API on affected browser configurations.

Executive priority

Prioritize patching where Python opens user-supplied URLs or where desktops and automation systems process external links. This is not evidenced as actively exploited, but the impact includes command execution consequences under specific conditions.

Technical view

The CVE describes incomplete mitigation of CVE-2026-4519. Certain browser types using webbrowser.open() could expand %action and inject commands into an underlying shell. CVSS 3.1 is 7.1: network reachable, high complexity, no privileges, user interaction required, with high confidentiality and integrity impact.

Likely exposure

Likely exposure is narrow but important: Python applications that call webbrowser.open() with untrusted or attacker-influenced URLs, especially where browser launcher configuration uses shell expansion. The bundle names Python Software Foundation CPython and references Python and Red Hat fixes.

Exploitation context

The provided bundle does not show active exploitation, and KEV is false. Exploitation would require user interaction and a vulnerable browser-launch path. Treat internet-facing workflows, help links, OAuth flows, or desktop automation that open external URLs as higher priority.

Researcher notes

Evidence is sufficient for root-cause direction but incomplete for exact affected release boundaries in this bundle. The affected data lists CPython with versions 0, 3.14.0a1, and 3.15.0a1, plus patch and advisory references. Avoid broad claims beyond those sources.

Mitigation direction

  • Update CPython or vendor Python packages using Python and Red Hat advisories.
  • Review Python applications that pass external URLs to webbrowser.open().
  • Avoid passing untrusted URLs to webbrowser.open() until patched.
  • Check vendor guidance for exact fixed package versions.
  • Prioritize systems handling URLs from users, email, web requests, or integrations.

Validation and detection

  • Inventory Python versions and vendor packages across servers and workstations.
  • Search code for webbrowser.open() and related browser-launch wrappers.
  • Trace whether URL inputs can be attacker-controlled.
  • Confirm patched CPython commits or vendor errata are applied.
  • Check browser launcher configuration for shell-backed expansion behavior.
Prepared
Confidence
medium
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

These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.

ATT&CK lookup starting points

Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.

cwe · medium confidence lookup

CWE-77: Command execution behavior lookup

Command injection weaknesses can lead defenders to review execution techniques and command interpreter telemetry. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.

Open ATT&CK lookup
cwe · medium confidence lookup

CWE-88: Command execution behavior lookup

Command injection weaknesses can lead defenders to review execution techniques and command interpreter telemetry. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.

Open ATT&CK lookup
description · low confidence lookup

Execution behavior lookup

The CVE wording references code or command execution, so execution technique review may help defensive triage. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program mapping.

Open ATT&CK lookup
cve · low confidence lookup

CVE-2026-4786 mapping review

Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.

Open ATT&CK lookup
Vulnerability profileCVE Program record
Severity
High
CVSS
7.1 (3.1)
Known Exploited
No
Published

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

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.

2CVSS vectors
5Timeline events
2ADP providers
49Source links

SSVC decision data

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

CVSS vector scores

2 official scores

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
7.1CVSS 3.1HighCVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:L1.65.5redhat-SADP
7CVSS 4.0HighCVSS:4.0/AV:L/AC:L/AT:P/PR:N/UI:A/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N——PSF

Vulnerability scoring details

Base CVSS 4.0 score

7High
CVSS 4.0 vector shape for CVE-2026-4786Attack VectorAttack ComplexityAttack RequirementsPrivileges RequiredUser InteractionVS ConfidentialityVS IntegrityVS AvailabilitySS ConfidentialitySS IntegritySS Availability

Vector: CVSS:4.0/AV:L/AC:L/AT:P/PR:N/UI:A/VC:H/VI:H/VA:N/SC:N/SI:N/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. ADP timelineredhat-SADP

    Made public.

  3. CVE publishedCVE Program

    The CVE record was published.

  4. ADP timelineredhat-SADP

    Reported to Red Hat.

  5. CVE updatedCVE Program

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

ADP provider summaries

CISA-ADPCISA ADP Vulnrichment
other:ssvc
redhat-SADPpython: cpython: Python: Arbitrary code execution via command injection in webbrowser.open() API
other:Red Hat severity ratingcvssV3_1
  • 2026-04-13T22:01:38.006Z: Reported to Red Hat.
  • 2026-04-13T21:52:19.036Z: Made public.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
Python Software FoundationCPython0, 3.14.0a1, 3.15.0a1unaffected
Weakness

CWE details

CWE-77CWE-88

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