What is CVE-2026-88921?

CVE-2026-88921 is MISP: Unescaped HTML Injection in PDF Report Element Rendering. The supplied enrichment data classifies it as Cross-site Scripting mapped to CWE-79 Cross-site Scripting; CWE-116 CWE-116.

Which versions are affected?

Affected product and version evidence is listed in the product table above. Current public advisories should be checked for exact version scope before patch targeting is finalized.

Is there active exploitation?

Active exploitation is not confirmed from current sources for CVE-2026-88921. If exploitation is not confirmed from current sources, teams should document that status and continue monitoring KEV, vendor, and telemetry updates.

No. CVE-2026-88921 is not listed in CISA KEV in the supplied enrichment data. KEV status should be monitored because it can change after initial disclosure or after exploitation becomes publicly confirmed.

Is there a public exploit?

A public PoC is not confirmed from current sources for CVE-2026-88921. Public exploit or PoC availability should raise triage priority, especially for exposed or business-critical systems.

How can defenders detect it?

Start with web/proxy/WAF logs, application logs, network IDS/IPS where available. Look for vulnerability-class behavior, product errors, suspicious authentication events, exploit probes, and abnormal process activity based only on evidence that applies to the affected product.

How should teams prioritize it?

Prioritize CVE-2026-88921 using CVSS 5.1, EPSS 0%, KEV status, public PoC status, and asset exposure. Internet-facing, privileged, or business-critical deployments should be handled first.

Are workarounds available?

Workarounds are not confirmed from current sources. Fixed-version evidence is listed in the mitigation section above.

Which threat actors are linked publicly?

No public threat actor linkage is confirmed from current sources. Do not attribute exploitation to a threat actor unless the source evidence explicitly supports that linkage.

What should be done in the next 24 hours?

Identify exposed assets running affected vendor/product/version combinations. Prioritize based on EPSS, PoC availability, and external exposure. Search available logs for exploit probes, errors, authentication anomalies, or suspicious child processes matching the vulnerability class. Open remediation tickets with affected assets, owners, evidence status, and detection coverage so decisions are traceable.

mediumCross-site Scripting

CVE-2026-88921

CVE-2026-88921 — MISP: Unescaped HTML Injection in PDF Report Element Rendering

MISP contains an HTML injection vulnerability in the MISPElementHTMLFormatterTool component, which is responsible for rendering MISP element references (attributes, objects, and tags) into inline HTML during PDF report export via the convert_markdown_to_pdf module. The attribute(), objectAttribute(), object(), and tag() methods interpolated user-controlled fields (attribute type, attribute value, object name, object relation, tag name, tag colour, and tag text colour) directly into HTML templates without applying HTML entity encoding. An authenticated user with the ability to create or modify MISP attributes, objects, or tags could embed arbitrary HTML markup in these fields. When a report containing such elements was exported to PDF, the unescaped content was rendered as live HTML rather than inert text, potentially injecting script tags, breaking the document structure, or altering the visual content of the exported report. Additionally, the attribute() method contained a template with hardcoded sample values ("domain-ip" and "google.com") instead of format placeholders, meaning every plain attribute reference in a PDF displayed the sample text rather than the actual indicator value, constituting a data-integrity defect in the exported document. The vulnerability requires an authenticated actor with write access to MISP elements and a subsequent PDF export of a report referencing those elements. The security impact is primarily to the integrity of the exported document and, depending on the HTML-to-PDF rendering engine, potential execution of injected markup during the conversion step. Version affected: ≤2.5.45

Published Sep 10, 2026Updated Sep 10, 2026Sources: NVD, MISP (CNA), GitHub, GitHub Security Advisory, SOCRadar CTI

Triage

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

Exploitation

Unreported

no source claims exploitation

EPSS

ahead of 0% of scored CVEs

Affects

MISP

CVSS base

5.1

medium

Remediation

The vendor's own words where we have them.

The fix applies HTML entity encoding (via the h() helper, which wraps htmlspecialchars with ENT_QUOTES and UTF-8) to every user-controlled value interpolated into the HTML templates in the MISPElementHTMLFormatterTool. This ensures that attribute types, values, object names, relations, tag names, and colour values are treated as inert data and cannot inject markup or break out of the surrounding span/style context. The hardcoded sample values in the attribute() template are replaced with proper %s format placeholders so that the actual element data is rendered. Comprehensive unit tests are ad…

First 24 hours

Ordered from the record's own fields — exposure first, because you cannot patch what you have not found.

Identify exposed assets running affected vendor/product/version combinations.
Prioritize based on EPSS, PoC availability, and external exposure.
Search available logs for exploit probes, errors, authentication anomalies, or suspicious child processes matching the vulnerability class.

Affected scope

Vendor, product and version as the advisories word them.

Vendor	Product	Versions	Status
MISP	MISP	unspecified to < 2.5.46	Vulnerable

Attack characteristics

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

Attack Complexity

Low

Attack Vector

Network

Privileges Req

Low

User Interaction

Every base score collected

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

Score	Version	Severity	Expl.	Impact	Source
5.1	CVSS 4.0	medium	—	—	MISP (CNA)

CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:P/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N

What this weakness leads to

MITRE's own consequences and mitigations for the weakness class — the authority's wording, not guidance derived from the CVSS vector.

MITRE

CWE-116 · Improper Encoding or Escaping of Output

Modify Application Data
Execute Unauthorized Code or Commands
Bypass Protection Mechanism

Mitigation: Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid. For example, consider using the ESAPI Encoding control [REF-45] or a similar tool, library, or framework. These will help the programmer encode outputs in a manner less prone to error. Alternately, use built-in functions, but consider using wrappers in case those functions are discovered to have a vulnerability.

CWE-79 · Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

Bypass Protection Mechanism
Read Application Data
Execute Unauthorized Code or Commands

Mitigation: Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid. Examples of libraries and frameworks that make it easier to generate properly encoded output include Microsoft's Anti-XSS library, the OWASP ESAPI Encoding module, and Apache Wicket.

Weakness & attack patterns

CWE-79Cross-site Scripting
CWE-116

Attack patterns reported against this CVE. The ATT&CK techniques below are inferred from its weakness class.

CAPEC-85 · AJAX FingerprintingCAPEC-591 · Reflected XSSCAPEC-63 · Cross-Site Scripting (XSS)CAPEC-209 · XSS Using MIME Type MismatchCAPEC-592 · Stored XSSCAPEC-588 · DOM-Based XSS

Detection

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

Prioritize edge telemetry for network-reachable MISP.

web/proxy/WAF logsapplication logsnetwork IDS/IPS

Timeline

What happened to this CVE, newest first — with the readings a source repeats on a schedule counted underneath rather than listed.

2026
Added · CVSS 3.1 5.1 (AV:N)
Sep 10, 2026 · NVD
Initial · CVE published
Sep 10, 2026 · NVD
Added · GHSA-6h22-87v4-49wc published (medium)
Sep 10, 2026 · GitHub Security Advisory
CVE published by MITRE.
Sep 10, 2026 · SOCRadar CTI

References

3 on the record

github.com/MISP/MISP/commit/949744a4b
Exploit, Third Party Advisory, Mitre
nvd.nist.gov/vuln/detail/CVE-2026-88921
NVD
github.com/advisories/GHSA-6h22-87v4-49wc
Exploit, Third Party Advisory

Elsewhere on this site

MISPevery CVE for this vendor
Cross-site Scriptingsame class
CWE-79other pages naming this weakness

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 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 record1

What should defenders know first?

CVE-2026-88921 is MISP: Unescaped HTML Injection in PDF Report Element Rendering, a medium vulnerability affecting MISP from MISP. The current evidence does not list it in CISA KEV, and the exploit status is: Active exploitation is not confirmed from current sources for CVE-2026-88921. Public exploit evidence is: A public PoC is not confirmed from current sources for CVE-2026-88921. The affected-version evidence is listed in the key facts and affected products tables. Defenders should first verify whether exposed or business-critical assets run those versions, then apply vendor patches or mitigations, restrict reachable attack surface, and preserve logs for detection review. CVSS 5.1 describes technical severity, while EPSS 0% helps estimate near-term exploit likelihood; neither replaces asset context. Unknown fields should remain explicit in tickets, and threat actor, IOC, victimology, or payload claims should not be added unless a cited source supports them. Monitor CISA KEV, vendor advisories, NVD changes, public PoC repositories, and internal telemetry for update triggers.