CVE-2026-4786: Incomplete mitigation of CVE-2026-4519, %action expansion for command injection to webbrowser.open()
Vulnerability summary
CVE-2026-4786 is a high (CVSS 7.1) vulnerability in python software foundation cpython. EPSS estimates a 0.29% chance of exploitation in the next 30 days, higher than 21.6% of scored vulnerabilities.
Not severe (CVSS 7, local access); no exploitation reported by the 5 checked sources
Source freshness unavailable
How is this decided?Advisory lineage
Upstream 0 · Downstream 59 · Related 26Timeline
- 13-04-2026PublishedVulnerability first disclosed.
- 13-08-2026Last modifiedVulnerability information updated.
Description
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.
CVSS metrics
11 scores · 8 sources · 2 versions- OSV · AlpineEcosystem advisory · calculated7.0HighCVSS:4.0/AV:L/AC:L/AT:P/PR:N/UI:A/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
- OSV · UbuntuEcosystem advisory · calculated7.0HighCVSS:4.0/AV:L/AC:L/AT:P/PR:N/UI:A/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N
- OSV · DebianEcosystem advisory · calculated7.0HighCVSS:4.0/AV:L/AC:L/AT:P/PR:N/UI:A/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
- OSV · WolfiEcosystem advisory · calculated7.0HighCVSS:4.0/AV:L/AC:L/AT:P/PR:N/UI:A/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N
- OSV · ChainguardEcosystem advisory · calculated7.0HighCVSS:4.0/AV:L/AC:L/AT:P/PR:N/UI:A/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N
- NVDNIST7.0HighCVSS:4.0/AV:L/AC:L/AT:P/PR:N/UI:A/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
- OSV · Red hatEcosystem advisory · calculated7.1HighCVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:L
- OSV · UbuntuEcosystem advisory · calculated7.1HighCVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:L
- NVDNIST7.1HighCVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:L
EPSS trend
Probability
0.29%
Chance of exploitation in the next 30 days
Percentile
22%
Versus all other CVEs
30-day change
Decrease -0.20 pp
From 0.48% on 04-10-2026
Known exploited
Compare KEV catalogsNot in the CISA KEV catalog.
Not in the ENISA CNW catalog.
Not in the CIRCL catalog.
Public exploits
0 foundNo public exploits indexed.
Weaknesses
CWE · root cause- CWE-77Improper Neutralization of Special Elements used in a CommandThe product constructs all or part of a command using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the intended command when it is sent to a downstream component.
- CWE-88Improper Neutralization of Argument Delimiters in a CommandThe product constructs a string for a command to be executed by a separate component in another control sphere, but it does not properly delimit the intended arguments, options, or switches within that command string.
Affected systems
Known conditions: local access, no authentication, user interaction (CVSS vector). Other conditions: not stated in public data.
Redhat16 products
- python< 0:2.7.5-94.el7_9.5 | < 0:2.6.6-70.el6_10.4
- python-debug< 0:2.7.5-94.el7_9.5
- python-debuginfo< 0:2.7.5-94.el7_9.5 | < 0:2.6.6-70.el6_10.4
- python-devel< 0:2.7.5-94.el7_9.5 | < 0:2.6.6-70.el6_10.4
- python-libs< 0:2.7.5-94.el7_9.5 | < 0:2.6.6-70.el6_10.4
Ubuntu14 products
- jythonAll versions (No fix recorded)
- pypy3All versions (No fix recorded)
- python2.7All versions (No fix recorded)
- python3.10< 3.10.12-1~22.04.16
- python3.11All versions (No fix recorded)
Chainguard6 products
- python-3.10< 3.10.20-r3
- python-3.11< 3.11.15-r2
- python-3.12< 3.12.14-r2
- python-3.13< 3.13.13-r2
- python-3.14< 3.14.4-r3
Wolfi5 products
- python-3.10< 3.10.20-r3
- python-3.11< 3.11.15-r2
- python-3.12< 3.12.14-r2
- python-3.13< 3.13.13-r2
- python-3.14< 3.14.4-r3
Debian3 products
- pypy3< 7.3.22+dfsg-1
- python3.13< 3.13.14-1
- python3.14< 3.14.5-1
Alpine1 product
- python3< 3.12.14-r0
Python software foundation1 product
- cpython< 3.10.21 | ≥ 3.11.0, < 3.11.16 | ≥ 3.12.0, < 3.12.14 | ≥ 3.13.0, < 3.13.14 | ≥ 3.14.0a1, < 3.14.5rc1 | ≥ 3.15.0a1, < 3.15.0b1
7 vendors · 46 products
References
70 links- mail.python.org/archives/list/security-announce@python.org/thread/JQDUNJVB4AQNTJECSUKOBDU3XCJIPSE5/Vendor AdvisoryARTICLEREPORTAdvisory
Show all 70 references
- github.com/python/cpythonPACKAGE