NukeViet: Multiple Anti-XSS Filter Bypasses Leading to Stored XSS in News Module
Summary
Two filter-bypass techniques in NukeViet\Core\Request::filterAttr() and NukeViet\Core\Request::unhtmlentities() allow a low-privileged user (any account with news post permission) to store and serve arbitrary JavaScript to any visitor of the affected page.
Affected Component
vendor/vinades/nukeviet/Core/Request.php — class NukeViet\Core\Request
Vulnerability Details
Bypass 1 — Form Feed character prefix (\x0C) before event handler name
The filterAttr() method blocks event-handler attributes using:
preg_match('/^on/i', $attrSubSet[0])
PHP's
trim() does
not strip the ASCII Form Feed character (
\x0C, U+000C). An attacker can prefix the attribute name with
\x0C so that
\x0Conerror does not match
/^on/. The HTML5 browser parser treats
\x0C as a valid whitespace separator and correctly activates the event handler.
Proof-of-concept payload (URL-encoded POST body field bodyhtml):
Bypass 2 — Decimal HTML entity tab ( ) inside javascript: URI
unhtmlentities() strips the hex-encoded tab via str_ireplace, but did not strip its decimal equivalent . The keyword-blocking regex /j\s*a\s*v\s*a\s*s\s*c\s*r\s*i\s*p\s*t/si uses \s* which does not match HTML entities. The value jav ascript:alert() passes the filter, is stored in the database, and is decoded by the browser into a working javascript: URI.
Proof-of-concept payload (inside a Markdown-style link):
Click me)
Impact
An authenticated attacker with news-posting permission can inject persistent JavaScript that executes in the browser of any user (including administrators) who views the affected article. This enables session cookie theft, credential harvesting, defacement, and further privilege escalation.
Patches
Fixed in commit ` by modifying vendor/vinades/nukeviet/Core/Request.php:
filterAttr() — strip all ASCII control characters (\x00–\x20) from the attribute name before the /^on/ check:
$attrSubSet[0] = preg_replace('/[\x00-\x20]/', '', strtolower($attrSubSet[0]));
unhtmlentities()` — strip decimal HTML entities for all ASCII control characters (0–31) before the keyword checks:
$value = preg_replace('/�*(?:3[01]|[12][0-9]|[0-9]);/', '', $value);
Workarounds
None. Update to the patched version.
Resources
- CWE-79: Improper Neutralization of Input During Web Page Generation (Cross-site Scripting)
- OWASP WSTG-INPV-02: Testing for Stored Cross Site Scripting
- OWASP Top 10 A03:2021 – Injection
What the EG score is made of (scorer v4.0: the three questions the 0–10 score mixes, published apart · methodology)
The EG score (8.7): severity, escalated by confirmed exploitation. This CVE's 8.7 is its impact severity (EG Severity), not escalated.
- EG Severity
- 8.7 HIGHCVSS-B, impact only: no KEV listing, EPSS or EG-KEV tier raises it.GitHub Security Advisory CVSS
- EG Likelihood
- Unknown (no EPSS on record)Unknown, not low: FIRST has published no EPSS probability for this CVE.
- Confirmed exploitation
- None on record (CISA KEV, EG-KEV Tier 1)Reported apart from the likelihood: an observed fact, not a probability.
- EG Priority
- SSVC Track at medium mission impactTrack at low or medium mission impact; Track* at high (mission-essential systems).CISA BOD 26-04: 14 days if the affected system is publicly exposed; Fix on system upgrade if it is not.Each input and its source, and whom BOD 26-04 binds: the SSVC and BOD 26-04 blocks below.
SSVC (CISA's decision table, applied by EchelonGraph)Track at low or medium mission impact; Track* at high (mission-essential systems).
A fix is available. Apply it within your standard update timelines.
Exploitation none (no CISA value, KEV listing or exploit code on record) · Automatable no (CISA's BOD 26-04 default) · Technical impact total (CISA's BOD 26-04 default). EchelonGraph holds no SSVC assessment of this CVE from CISA: none of these inputs is from Vulnrichment. EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE. Mission impact is CISA's Mission & Well-being decision point, and only you can judge it. CISA's table makes it high when Mission Prevalence is Essential — the vulnerable component "directly provides capabilities that constitute at least one MEF for at least one entity" (MEF: mission essential function) — or when Public Well-Being Impact is Irreversible: "multiple fatalities are likely", the cyber-physical system "is likely lost or destroyed", "extreme or serious externalities" are imposed on other parties, or social systems such as elections or the financial grid "are destabilized and potentially collapse". CISA's decision table
BOD 26-04 (CISA's remediation timeline, Table 1)14 days if the affected system is publicly exposed; Fix on system upgrade if it is not.
The score's inputs: In CISA KEV no (CISA's KEV catalog) · Automatable no (CISA's BOD 26-04 default) · Technical impact total (CISA's BOD 26-04 default). Where an input reads “CISA's BOD 26-04 default”, no one has published it for this CVE, and CISA's implementation guidance says: “If “Automatable” and “Technical Impact” information items about a CVE ID are not available and the CVE ID is not in the KEV Catalog, CISA will treat its values as “no” and “total,” respectively, until CISA or a third party provides metadata about the CVE ID. CISA will always provide the Vulnrichment data for a CVE ID listed in the KEV Catalog.” Whether your system is publicly exposed is yours to answer. BOD 26-04 binds US Federal Civilian Executive Branch agencies; for anyone else it is CISA's published timeline, a reference rather than an obligation. The directive · how EchelonGraph applies it