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Python Liquid EUVDEUVD-2026-42693

| CVE-2026-55865 HIGH
Loop with Unreachable Exit Condition (Infinite Loop) (CWE-835)
2026-06-19 https://github.com/jg-rp/liquid GHSA-vq2f-vcc9-j8mv
7.1
CVSS 4.0 · Vendor: https://github.com/jg-rp/liquid
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Severity by source

Vendor (https://github.com/jg-rp/liquid) PRIMARY
7.1 HIGH
CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/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
vuln.today AI
6.5 MEDIUM

Attacker must be able to submit a template (PR:L) to a network-reachable parser with a trivial payload (AC:L); impact is availability-only (A:H, C:N/I:N) with no scope change.

3.1 AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
4.0 AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

Primary rating from Vendor (https://github.com/jg-rp/liquid).

CVSS VectorVendor: https://github.com/jg-rp/liquid

CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/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
Attack Vector
Network
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
X

Lifecycle Timeline

6
Analysis Updated
Jul 09, 2026 - 21:28 vuln.today
v3 (cvss_changed)
Analysis Updated
Jul 09, 2026 - 21:28 vuln.today
v2 (cvss_changed)
Re-analysis Queued
Jul 09, 2026 - 21:22 vuln.today
cvss_changed
CVSS changed
Jul 09, 2026 - 21:22 NVD
7.1 (HIGH)
Source Code Evidence Fetched
Jun 19, 2026 - 21:47 vuln.today
Analysis Generated
Jun 19, 2026 - 21:47 vuln.today

DescriptionCVE.org

Impact

Given a malformed {% case %} tag without associated {% when %} or {% else %} block, and no terminating {% endcase %} tag, Python Liquid hangs in an infinite loop at parse time. This allows malicious template authors to craft templates for a denial of service attack.

Patches

The issue is fixed in version 2.2.1 with the correction of the liquid.TokenStream.eof attribute. The kind and value of the special EOF token are now the same, so either can be tested against liquid.token.TOKEN_EOF.

Workarounds

Manually correct the definition of liquid.TokenStream.eof before parsing any templates.

python
import liquid
from liquid.token import TOKEN_EOF

liquid.stream.TokenStream.eof = liquid.Token(TOKEN_EOF, TOKEN_EOF, -1, "")
# ...

AnalysisAI

{% case %} tag that has no {% when %}, {% else %}, or closing {% endcase %}. Because the loop occurs at parse time, any application that renders untrusted or user-supplied Liquid templates can be frozen with a payload as small as {% case x %}. …

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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata

Access
Obtain template-authoring access (PR:L)
Delivery
Submit template '{% case x %}' with no when/endcase
Exploit
Parser enters infinite loop at parse time
Execution
CPU pinned, worker hangs
Persist
Repeat to exhaust worker pool
Impact
Service denial

Vulnerability AssessmentAI

Exploitation Exploitation requires that the target application parse a Liquid template that the attacker can control, using python-liquid before 2.2.1, and that the template contain a malformed `{% case %}` tag lacking any `{% when %}`/`{% else %}` branch and a closing `{% endcase %}` (e.g., `{% case x %}`). … Additional conditions and limiting factors are described in the full assessment.
Risk Assessment The vendor CVSS 4.0 vector (CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H, score 7.1) captures the profile well: network-reachable, low complexity, low privileges required (the actor must be able to submit a template), no user interaction, and impact limited to high availability loss with zero confidentiality or integrity effect. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in.
Exploit Scenario A web application lets tenants define custom Liquid templates for notifications or reports and renders them with python-liquid < 2.2.1. An attacker with a low-privilege account saves the template `{% case x %}` with no `{% when %}`/`{% endcase %}`; when the server parses it, the worker thread pins CPU and hangs indefinitely, and repeating this across workers exhausts the request pool and denies service. …
Remediation Vendor-released patch: upgrade python-liquid to version 2.2.1 or later (release https://github.com/jg-rp/liquid/releases/tag/v2.2.1, fix commit 26db8931cf35e8433c1ca506fc32c3bb62f743d4), which makes the malformed `{% case %}` template raise a `LiquidSyntaxError` instead of looping. … Detailed patch versions, workarounds, and compensating controls in full report.

Recommended ActionAI

Within 24 hours: Identify all systems and applications using Liquid template engine; cross-reference with asset inventory and prioritize those processing untrusted template input. …

Sign in for detailed remediation steps and compensating controls.

Threat intelligence, references, and detailed analysis are available after sign-in.

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EUVD-2026-42693 vulnerability details – vuln.today

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