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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

CPython’s earlier fix for CVE-2026-4519 was incomplete. In applications that open attacker-influenced URLs, a specially formed URL may cause certain browser configurations to pass unintended commands to a shell. Successful abuse requires user interaction, but could compromise confidentiality and integrity and cause limited disruption.

Executive priority

Treat as a high-priority targeted remediation, not evidence of an internet-wide emergency. Quickly identify applications combining vulnerable CPython, webbrowser.open(), untrusted URLs, and affected browser configurations. Patch exposed systems first and reduce privileges while remediation proceeds.

Technical view

CVE-2026-4786 is a command-injection bypass involving %action expansion in webbrowser.open(). For certain browser types, crafted URL content can reach the underlying shell despite the earlier mitigation. It is rated CVSS 3.1 7.1: network-reachable, high complexity, no privileges required, user interaction required, with high confidentiality and integrity impact.

Likely exposure

Exposure depends on both runtime and application behavior. Prioritize systems using affected CPython builds where untrusted or remotely supplied URLs reach webbrowser.open(), particularly with shell-backed browser configurations. The supplied version data does not define complete affected or fixed ranges, so confirm exact package status through Python or distribution advisories.

Exploitation context

The source bundle does not report CISA KEV inclusion or active exploitation. Exploitation requires a vulnerable application flow, a relevant browser type, attacker-controlled URL content containing %action, and user interaction. These prerequisites reduce broad exploitability, but successful command injection could execute with the application user’s permissions.

Researcher notes

This is an incomplete mitigation of CVE-2026-4519, mapped to CWE-77 and CWE-88. Analysis should distinguish CPython library presence from reachable vulnerable behavior. The bundle references several patches but does not map them to definitive fixed release numbers. No active-exploitation claim is supported.

Mitigation direction

  • Apply the applicable CPython or operating-system vendor security update addressing CVE-2026-4786.
  • Review vendor advisories to determine fixed versions; the supplied affected-version list is incomplete.
  • Prevent untrusted URLs from reaching webbrowser.open() until affected runtimes are updated.
  • Avoid shell-backed custom browser configurations where operationally feasible.
  • Restrict the application account’s privileges to limit impact from command execution.

Validation and detection

  • Inventory CPython versions and distribution packages on systems invoking webbrowser.open().
  • Identify application paths that pass remote, user-controlled, or indirectly controlled URLs to webbrowser.open().
  • Check browser registrations and configurations for command templates that invoke an underlying shell.
  • Confirm installed packages include the applicable vendor fix or referenced CPython patch.
  • Run a safe regression test verifying %action remains literal and cannot trigger command execution.
Prepared
Confidence
high
Sources
6

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
50Source 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, 3.11.0, 3.12.0, 3.13.0, 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.