CVE Intelligence
Low Injection

CVE-2026-71438 — Mermaid configuration APIs allow prototype pollution

Mermaid is a JavaScript tool that uses Markdown-inspired text to create and modify diagrams and charts. Prior to 10.9.8 and 11.16.1, Mermaid's configuration setters (mermaid.initialize, mermaidAPI.setConfig, and mermaidAPI.updateSiteConfig) merge caller-supplied configuration into Mermaid's internal config using the assignWithDepth deep-merge helper, which is vulnerable to prototype pollution. This is only exploitable if an application forwards untrusted data directly into one of these configuration entry points, which is outside their documented usage; diagram-supplied configuration (e.g. %%{init: {}}%% or YAML frontmatter) is not affected. This issue is fixed in versions 10.9.8 and 11.16.1.

Published Aug 6, 2026 · Updated Oct 15, 2026 · Sources: NIST National Vulnerability Database, CVE Program (cve.org) e CISA ADP · CNA: GitHub_M

Who exploits it and how urgent it is

A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.

No exploitation signal in the sources consulted so far.
How the score was calculated
  • EPSS 0.4% (30-day exploitation probability)+4

The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.

Exploitation
Not confirmed
Not in CISA KEV — an absence of record, not proof it is unexploited.
EPSS FIRST
0.35%
ahead of 27% of scored CVEs · Oct 15, 2026
Affects
Mermaid-js
Mermaid
CVSS base
2.4
Low · 2 source(s)

CISA SSVC assessment CISA

Three decision points CISA publishes for the CVEs it assesses (SSVC 2.0.3). A stakeholder decision, not a severity score.

Exploitation
None
none · proof-of-concept · active
Automatable
No
can an attacker script the kill-chain steps
Technical impact
Partial
partial · total control of the vulnerable component

Remediation

Fixes and mitigations documented by the sources — linked to the original advisory.

No fix documented by the sources we poll. That does not mean none exists: check the vendor advisory.

First 24 hours

Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.

  1. Identify exposed assets running the affected vendor/product/version combinations (Mermaid-js Mermaid).
  2. No fix documented in the sources: reduce exposure and monitor the vendor advisory.
  3. Exploitation requires user interaction: tighten email/web filtering and warn affected users.
  4. Search available logs for exploit probes matching the vulnerability class (injection), errors and authentication anomalies.

Affected scope

Vendor, product and versions as the sources word them.

VendorProductVersionsStatusSource
Mermaid-js Mermaid version < 10.9.8version >= 11.0.0-alpha.1, < 11.16.1 Vulnerable CVE Program (cve.org) e CISA ADP

Attack characteristics

The CVSS vector, decoded. It describes the attack, not your exposure to it.

Attack vector
Local
Attack complexity
Low
Attack requirements
Present
Privileges required
High
User interaction
Active
Scope
X
Confidentiality (vulnerable system)
None
Integrity (vulnerable system)
Low
Availability (vulnerable system)
Low
Confidentiality (subsequent)
High
Integrity (subsequent)
High
Availability (subsequent)
High

Every base score collected

Sources score independently and may disagree; each row says who scored it and under which version.

ScoreVersionSeverityExpl.ImpactScored by
2.4 CVSS 4.0 Low — — security-advisories@github.com via NIST National Vulnerability Database
2.4 CVSS 4.0 Low — — GitHub_M via CVE Program (cve.org) e CISA ADP
CVSS:4.0/AV:L/AC:L/AT:P/PR:H/UI:A/VC:N/VI:L/VA:L/SC:H/SI:H/SA:H/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 (score shown at the top: security-advisories@github.com)

Weakness MITRE

Weakness class according to MITRE’s CWE catalog.

CWE-1321 · Prototype Pollution

Other CVEs with this weakness →

Detection

Read off the CVSS vector and the weakness class. Starting points, not tested rules.

  • Local/physical vector: focus on endpoint telemetry (EDR) from affected hosts.
  • Look for parameters with command/query metacharacters and unexpected child processes of the service.
endpoint telemetry (EDR)application logs

Timeline

What happened to this CVE, newest first.

  • 2026
  • Affected products added · mermaid-js/mermaid
    Oct 15, 2026 · CVE Program (cve.org) e CISA ADP
  • SSVC assessment updated
    Oct 15, 2026 · CVE Program (cve.org) e CISA ADP
  • Record published
    Oct 15, 2026
  • CVSS changed · 2.4
    Oct 15, 2026 · NIST National Vulnerability Database
  • Source status changed · → Awaiting Analysis
    Oct 15, 2026 · NIST National Vulnerability Database
  • Record created in this database
    Oct 15, 2026 · NIST National Vulnerability Database
  • CVE published
    Aug 6, 2026 · GitHub_M

Source activity

Repeated readings are counted rather than listed.

  • 1× Official description updated · Oct 15, 2026 – Oct 15, 2026

References

6 on the record

Elsewhere on this site

Mermaid-js
every CVE for this vendor
Injection
same class
CWE-1321
other pages naming this weakness

Related CVEs (same products)

  • CVE-2026-71439 Mermaid radar diagrams are vulnerable to DoS Aug 6, 2026
  • CVE-2026-71436 Mermaid XY Charts are vulnerable to an infinite loop DoS Aug 6, 2026
  • CVE-2026-71437 Mermaid Architecture diagrams are vulnerable to prototype pollution Aug 6, 2026
  • CVE-2026-50159 Mermaid allows CSS injection applying to sibling elements of the diagram Aug 6, 2026
  • CVE-2026-41159 Mermaid: Improper sanitization of configuration leads to CSS injection May 29, 2026
  • CVE-2026-41150 Mermaid Gantt Charts are vulnerable to an Infinite Loop DoS May 29, 2026

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

  • No fixed version, patch or mitigation documented.
  • No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
  • No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
  • No exploit packet captures, log samples, or incident case IDs supplied.

Answered from this record

Text assembled only from the fields above — no additional claims.

What should defenders know first?

CVE-2026-71438 is "Mermaid configuration APIs allow prototype pollution", rated Low. It affects Mermaid (Mermaid-js); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 2.4 describes technical severity. EPSS 0.35% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.

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