CVE-2026-21132

Executive Summary

CVE-2026-21132 is an improper input validation vulnerability in Samsung Internet versions prior to 30.0.5.24 that allows remote attackers to inject arbitrary script. Successful exploitation requires user interaction, meaning a victim must visit a malicious or compromised web page or interact with crafted content rendered in the affected browser. The impact is client-side script injection within the browsing context, which can lead to session manipulation, content spoofing, or data exfiltration from pages the user visits.

Technical Analysis

The vulnerability class is improper input validation (CWE-20) leading to arbitrary script injection in Samsung Internet prior to version 30.0.5.24. The NVD description explicitly states that the flaw allows "remote attackers to inject arbitrary script" and that "user interaction is required for triggering this vulnerability."

At the vulnerability-class level, improper input validation means the browser fails to correctly sanitize, encode, or validate attacker-controllable input before it is processed or rendered. When that unvalidated input reaches a context where script can execute — for example, a document rendering context, a URL-handling path, or an internal browser surface — the injected script runs with the privileges of the affected browsing context. Because the description does not name specific functions, parameters, URL schemes, or DOM sinks, the precise injection point cannot be determined from available data. No public exploit code, Nuclei template, or PoC is available (POC_STATUS: None), and the CWE is not formally assigned by the CNA (provided as N/A; CWE-20 is the best-fit classification for input validation failure).

Attack surface: the Samsung Internet application on Android. The vulnerable component is client-side (the browser itself), and exploitation depends on a victim rendering or interacting with attacker-supplied content. There is no evidence that this flaw enables remote code execution on the device, nor is there server-side impact described. It is therefore a client-side script injection issue confined to the browser's rendering/execution context, with scope potentially changed (S:C) if injected script can cross a trust boundary within the browser.

Insufficient technical detail is available in the source data to describe the specific code path, the input vector (e.g., URL parameter, deep link, or DOM source), or the exact sink where script is injected. Any statement naming specific functions or endpoints would be speculative and is deliberately omitted.

Exploitation Scenarios

The following attack chain is inferred from the vulnerability class (improper input validation → arbitrary script injection) and the stated requirement for user interaction. No public PoC is available; the steps below describe the attack at the vulnerability-class level.

1. Reconnaissance / target identification: An attacker identifies users of Samsung Internet on Android with a version below 30.0.5.24. This can be done through fingerprinting a web property, ad network targeting, or directing traffic to attacker-controlled pages. Because the flaw is client-side, the attacker does not need to locate a specific server — they need the victim to load crafted content in the vulnerable browser.

2. Triggering the flaw class: The attacker crafts input that the browser fails to validate or sanitize. The victim must interact — for example, by navigating to an attacker-controlled page, clicking a crafted link, or interacting with injected content. User interaction is explicitly required per the NVD description.

3. Payload / execution method: Because input validation is improper, attacker-supplied content containing script is not correctly neutralized, and the script executes in the context in which the unvalidated input is processed. At the class level, this is script injection: the attacker's script runs as if it originated from the affected context. The exact injection mechanism (DOM-based, reflected, or otherwise) is not specified in the available data and is not asserted here.

4. Post-exploitation impact: Once script executes in the browsing context, the attacker can act within the scope the browser grants that context — for example, reading or modifying page content the user can access, interacting with the page's session state, redirecting the user, or capturing data entered into the affected page. The description does not establish device-level code execution or persistence; impact should be scoped to the client-side injection context.

Impact Assessment

No CVSS score or vector was provided by the source (CVSS: N/A), and no EPSS score has been assigned by FIRST.org. The vector shown in METADATA (CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N) is an analytical estimate consistent with a remote, user-interaction-required client-side injection issue with potential scope change and limited confidentiality/integrity impact; it is not a vendor-published score and should be treated as provisional.

Business impact: affected systems are Android devices running Samsung Internet below 30.0.5.24. Given the large installed base of Samsung Internet on Samsung and non-Samsung Android devices, the population of potentially affected users may be substantial. Blast radius is per-user and per-session rather than server-side: an attacker cannot use this flaw alone to compromise a backend service. However, in enterprise contexts where users access web applications, SaaS dashboards, or internal portals through Samsung Internet on managed or BYOD devices, injected script could lead to credential or token exposure within a page context, content tampering, or phishing-style manipulation. The required user interaction lowers the likelihood of mass automated exploitation but does not eliminate targeted phishing or watering-hole risk.

Because no CISA KEV listing exists and no exploit code or PoC is public, exploitation in the wild is not evidenced by the provided data. Residual risk is driven primarily by the unpatched state for users who remain below 30.0.5.24 and by the absence of vendor advisories or patch tracking data in the feeds reviewed.

Detection Guidance

Sigma Rule

title: Samsung Internet Script Injection Attempt (CVE-2026-21132)
id: 3f7c1a92-0b21-4e3d-9a55-7b2c1d4e8f01
status: experimental
description: Detects indicators of suspicious script injection or script-bearing content delivered to Samsung Internet below 30.0.5.24.
references:
  - https://nvd.nist.gov/vuln/detail/CVE-2026-21132
author: valtersit.com
date: 2026/01/01
logsource:
  category: proxy
  product: web
detection:
  selection_ua:
    c-user-agent|contains:
      - 'SamsungBrowser/'
  selection_version:
    c-user-agent|contains:
      - 'SamsungBrowser/2'
      - 'SamsungBrowser/30.0.0'
      - 'SamsungBrowser/30.0.1'
      - 'SamsungBrowser/30.0.2'
      - 'SamsungBrowser/30.0.3'
      - 'SamsungBrowser/30.0.4'
  selection_payload:
    c-uri|contains:
      - '<script'
      - 'javascript:'
      - 'onerror='
      - 'onload='
  condition: selection_ua and selection_version and selection_payload
falsepositives:
  - Legitimate applications passing script-like parameters
level: medium
tags:
  - attack.t1203
  - cve.2026.21132

YARA Rule

rule CVE_2026_21132_SamsungInternet_ScriptInjection
{
    meta:
        description = "Detects script injection payload patterns associated with CVE-2026-21132 affecting Samsung Internet < 30.0.5.24"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2026-21132"
        author = "valtersit.com"
        date = "2026-01-01"
        severity = "medium"
    strings:
        $samsung = "SamsungBrowser" nocase
        $ver_prefix = "SamsungBrowser/2" ascii
        $script1 = "<script" nocase
        $script2 = "javascript:" nocase
        $handler1 = "onerror=" nocase
        $handler2 = "onload=" nocase
        $handler3 = "onmouseover=" nocase
    condition:
        $samsung or $ver_prefix or (2 of ($script*) or 1 of ($handler*))
}

Suricata IDS Rule

alert http any any -> any any (msg:"CVE-2026-21132 Samsung Internet Script Injection Attempt"; flow:established,to_client; http.user_agent; content:"SamsungBrowser/"; http.user_agent; pcre:"/SamsungBrowser\/(2|30\.0\.[0-4])/R"; http.response_body; content:"<script"; nocase; sid:202621132; rev:1; reference:cve,2026-21132; classtype:web-application-attack; metadata:affected_product Samsung_Internet, attack_target Client_Endpoint, deployment Perimeter, signature_severity Minor;)

Elastic Detection

sequence by source.ip, user_agent.original with maxspan=5m
  [network where network.protocol == "http" and
     user_agent.original : "SamsungBrowser/*" and
     user_agent.original regex "SamsungBrowser/(2|30\\.0\\.[0-4])"]
  [network where http.response.body : ("*<script*" or "*javascript:*" or "*onerror=*")]

Splunk SPL Query

index=proxy OR index=web
| eval ua=coalesce(http_user_agent, user_agent, c_user_agent)
| where match(ua, "SamsungBrowser/(2|30\.0\.[0-4])")
| where match(coalesce(uri, url, http_uri), "(?i)(<script|javascript:|onerror=|onload=)")
| stats count min(_time) as first_seen max(_time) as last_seen by src_ip, dest_host, uri, ua
| convert ctime(first_seen) ctime(last_seen)
| sort - count

Wazuh OSSEC Rule

<group name="web,cve-2026-21132,">
  <rule id="100321" level="8">
    <decoded_as>web-accesslog</decoded_as>
    <field name="user_agent">SamsungBrowser/</field>
    <field name="url" type="pcre2">(?i)(&lt;script|javascript:|onerror=|onload=)</field>
    <description>CVE-2026-21132: Potential script injection delivered to vulnerable Samsung Internet client.</description>
    <mitre>
      <id>T1203</id>
    </mitre>
  </rule>
</group>

Mitigation & Patch Guidance

Patch confidence: 0/4 (UNPATCHED — no patch evidence from any tracked source).

1. Immediate mitigations:

• Update Samsung Internet to version 30.0.5.24 or later as directed by the NVD description; this is the primary remediation step. Where the update cannot be applied immediately, restrict use of the vulnerable browser version for accessing sensitive web applications (SaaS dashboards, internal portals, webmail, SSO flows).
• Enforce browser hygiene through MDM/EMM: where feasible, blacklist or set a minimum-version policy for Samsung Internet on managed Android devices, or require an alternative managed browser for sensitive corporate web access.
• Apply network-layer filtering (the Suricata/Sigma logic above) to flag script-bearing responses to vulnerable user agents, and raise user awareness of phishing/watering-hole links that require interaction to trigger client-side injection.

2. Patch/upgrade steps:

• No vendor advisory, patch reference, or fixed package has been confirmed by tracked sources (Patch Sources: empty; Vendor Fix: N/A). The only concrete version guidance comes from NVD: upgrade to Samsung Internet 30.0.5.24 or later. Validate availability through the official Google Play listing or Samsung's app distribution channel before rolling out, since no vendor advisory was located during analysis.
• After upgrade, verify the installed version in the browser's settings/about screen to confirm the build is at or above 30.0.5.24.

3. Long-term hardening:

• Establish a browser-version minimum baseline for corporate web access and monitor endpoint inventory for outdated browsers (including Samsung Internet) alongside other client software.
• Deploy Content Security Policy and output-encoding controls on owned web properties to reduce the impact of client-side script injection against any browser, not only the vulnerable version.
• Track CVE feeds for Samsung Internet and integrate the detection content above into SOC pipelines; reassess severity once a CVSS score or EPSS value becomes available and monitor for the appearance of public PoC code.

References

• NVD — CVE-2026-21132: https://nvd.nist.gov/vuln/detail/CVE-2026-21132
• CWE-20 — Improper Input Validation: https://cwe.mitre.org/data/definitions/20.html
• MITRE ATT&CK T1203 — Exploitation for Client Execution: https://attack.mitre.org/techniques/T1203/
• FIRST EPSS (score not yet assigned at time of writing): https://www.first.org/epss/
• Samsung Internet (official app/version source): https://play.google.com/store/apps/details?id=com.sec.android.app.sbrowser

No CISA KEV listing, public PoC, exploit code, Nuclei template, or threat-actor campaign has been identified in the available data for CVE-2026-21132. Exploitation in the wild is not evidenced by tracked sources.