Vulnerability-Lookup

CVE-2026-26028 (GCVE-0-2026-26028)

Vulnerability from cvelistv5 – Published: 2026-05-20 18:51 – Updated: 2026-05-20 19:33

Title

CryptPad: Sanitizer Bypass in Diffmarked.js Allows Arbitrary HTML Injection and Potential XSS

Summary

CryptPad is an end-to-end encrypted collaborative office suite. In versions prior to 2026.2.0, the HTML sanitizer in Diffmarked.js can be bypassed due to incomplete attribute filtering on restricted tags. The sanitizer validates only the src attribute of <iframe>, <video>, and <audio> elements, leaving all other attributes unchecked. As a result, an attacker can inject arbitrary HTML through srcdoc, completely defeating CryptPad's intended bounce sandboxing and enabling link injection or other interactive content within user-controlled documents. The root cause lies in how the sanitizer classifies and enforces tag restrictions: although it defines both forbidden and restricted tag lists, <iframe> is treated as "restricted" rather than "forbidden." Enforcement then inspects only the src attribute, so pairing a benign blob: src with a malicious srcdoc results in unrestricted rendering. This issue has been fixed in version 2026.2.0.

Severity

6.1 (Medium)


                        
                          CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

CWE

CWE-116 - Improper Encoding or Escaping of Output
CWE-79 - Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

Assigner

GitHub_M

References

2 references

URL	Tags
https://github.com/cryptpad/cryptpad/security/adv…	x_refsource_CONFIRM
https://github.com/cryptpad/cryptpad/releases/tag…	x_refsource_MISC

Impacted products

1 product

Vendor	Product	Version
cryptpad	cryptpad	Affected: < 2026.2.0

Show details on NVD website

JSON

To clipboard

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FKIE_CVE-2026-26028

Vulnerability from fkie_nvd - Published: 2026-05-20 20:16 - Updated: 2026-05-21 16:04

Severity

6.1 (Medium) - CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

Summary

References

	URL	Tags
	security-advisories@github.com	https://github.com/cryptpad/cryptpad/releases/tag/2026.2.0
	security-advisories@github.com	https://github.com/cryptpad/cryptpad/security/advisories/GHSA-g2g4-47gv-p72v

Impacted products

	Vendor	Product	Version

JSON

To clipboard

{
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "CryptPad is an end-to-end encrypted collaborative office suite. In versions prior to 2026.2.0, the HTML sanitizer in Diffmarked.js can be bypassed due to incomplete attribute filtering on restricted tags. The sanitizer validates only the src attribute of \u003ciframe\u003e, \u003cvideo\u003e, and \u003caudio\u003e elements, leaving all other attributes unchecked. As a result, an attacker can inject arbitrary HTML through srcdoc, completely defeating CryptPad\u0027s intended bounce sandboxing and enabling link injection or other interactive content within user-controlled documents. The root cause lies in how the sanitizer classifies and enforces tag restrictions: although it defines both forbidden and restricted tag lists, \u003ciframe\u003e is treated as \"restricted\" rather than \"forbidden.\" Enforcement then inspects only the src attribute, so pairing a benign blob: src with a malicious srcdoc results in unrestricted rendering. This issue has been fixed in version 2026.2.0."
    }
  ],
  "id": "CVE-2026-26028",
  "lastModified": "2026-05-21T16:04:53.813",
  "metrics": {
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      {
        "cvssData": {
          "attackComplexity": "LOW",
          "attackVector": "NETWORK",
          "availabilityImpact": "NONE",
          "baseScore": 6.1,
          "baseSeverity": "MEDIUM",
          "confidentialityImpact": "LOW",
          "integrityImpact": "LOW",
          "privilegesRequired": "NONE",
          "scope": "CHANGED",
          "userInteraction": "REQUIRED",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N",
          "version": "3.1"
        },
        "exploitabilityScore": 2.8,
        "impactScore": 2.7,
        "source": "security-advisories@github.com",
        "type": "Secondary"
      }
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  },
  "published": "2026-05-20T20:16:36.760",
  "references": [
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/cryptpad/cryptpad/releases/tag/2026.2.0"
    },
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/cryptpad/cryptpad/security/advisories/GHSA-g2g4-47gv-p72v"
    }
  ],
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  "vulnStatus": "Deferred",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-79"
        },
        {
          "lang": "en",
          "value": "CWE-116"
        }
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      "source": "security-advisories@github.com",
      "type": "Primary"
    }
  ]
}

GHSA-G2G4-47GV-P72V

Vulnerability from github – Published: 2026-05-26 19:05 – Updated: 2026-05-26 19:05

Summary

CryptPad has a Sanitizer Bypass in Diffmarked.js that Allows Arbitrary HTML Injection and Potential XSS

Details

Summary

CryptPad’s HTML sanitizer in Diffmarked.js can be bypassed due to incomplete filtering of restricted tags. Because the sanitizer only validates the src attribute of <iframe> <video>, and <audio> elements, and does not restrict other attributes, an attacker can inject arbitrary HTML through srcdoc. This completely defeats CryptPad’s intended bounce sandboxing and allows link injection or other interactive content inside user-controlled documents.

Details

The sanitizer defines forbidden and restricted tags but treats as “restricted” instead of “forbidden”:

https://github.com/cryptpad/cryptpad/blob/0dd3c1f53d56dffb06651b86ead6b9b387920173/www/common/diffMarked.js#L403-L407 The actual enforcement only checks the src attribute, nothing else:

https://github.com/cryptpad/cryptpad/blob/0dd3c1f53d56dffb06651b86ead6b9b387920173/www/common/diffMarked.js#L445-L449

Because only src is validated, adding a benign blob: src but malicious srcdoc results in unrestricted rendering.

PoC

An attacker can embed arbitrary HTML, including clickable external links, images, or interactive content, completely bypassing CryptPad’s bounce mechanism and sanitization:

<iframe src=blob: srcdoc="<a href=https://attacker.com target=_blank>CLICK ME</a>"></iframe>

Although CSP is strict, CryptPad exposes several same-origin gadgets that can execute attacker-controlled code.

For example, jscolor.js dynamically evaluates user-provided options: https://github.com/cryptpad/cryptpad/blob/0dd3c1f53d56dffb06651b86ead6b9b387920173/www/common/jscolor.js#L65-L71

Impact

Sanitizer bypass, HTML injection and potentially XSS.

Severity

6.1 (Medium)


                  
                    CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N

Show details on source website

JSON

To clipboard

{
  "affected": [
    {
      "package": {
        "ecosystem": "npm",
        "name": "cryptpad"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "last_affected": "5.9.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-26028"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-79",
      "CWE-116"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-05-26T19:05:10Z",
    "nvd_published_at": "2026-05-20T20:16:36Z",
    "severity": "MODERATE"
  },
  "details": "### Summary\nCryptPad\u2019s HTML sanitizer in Diffmarked.js can be bypassed due to incomplete filtering of restricted tags.\nBecause the sanitizer only validates the src attribute of `\u003ciframe\u003e` `\u003cvideo\u003e`, and `\u003caudio\u003e` elements,  and does not restrict other attributes, an attacker can inject arbitrary HTML through srcdoc. This completely defeats CryptPad\u2019s intended bounce sandboxing and allows link injection or other interactive content inside user-controlled documents.\n\n### Details\nThe sanitizer defines forbidden and restricted tags but treats \u003ciframe\u003e as \u201crestricted\u201d instead of \u201cforbidden\u201d:\n\nhttps://github.com/cryptpad/cryptpad/blob/0dd3c1f53d56dffb06651b86ead6b9b387920173/www/common/diffMarked.js#L403-L407\nThe actual enforcement only checks the src attribute, nothing else:\n\nhttps://github.com/cryptpad/cryptpad/blob/0dd3c1f53d56dffb06651b86ead6b9b387920173/www/common/diffMarked.js#L445-L449\n\nBecause only src is validated, adding a benign blob: src but malicious srcdoc results in unrestricted rendering.\n### PoC\n\nAn attacker can embed arbitrary HTML, including clickable external links, images, or interactive content, completely bypassing CryptPad\u2019s bounce mechanism and sanitization:\n\n```html\n\u003ciframe src=blob: srcdoc=\"\u003ca href=https://attacker.com target=_blank\u003eCLICK ME\u003c/a\u003e\"\u003e\u003c/iframe\u003e\n```\n\nAlthough CSP is strict, CryptPad exposes several same-origin gadgets that can execute attacker-controlled code.\n\nFor example, `jscolor.js` dynamically evaluates user-provided options:\nhttps://github.com/cryptpad/cryptpad/blob/0dd3c1f53d56dffb06651b86ead6b9b387920173/www/common/jscolor.js#L65-L71\n\n### Impact\nSanitizer bypass, HTML injection and potentially XSS.",
  "id": "GHSA-g2g4-47gv-p72v",
  "modified": "2026-05-26T19:05:10Z",
  "published": "2026-05-26T19:05:10Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/cryptpad/cryptpad/security/advisories/GHSA-g2g4-47gv-p72v"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-26028"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/cryptpad/cryptpad"
    },
    {
      "type": "WEB",
      "url": "https://github.com/cryptpad/cryptpad/releases/tag/2026.2.0"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "CryptPad has a Sanitizer Bypass in Diffmarked.js that Allows Arbitrary HTML Injection and Potential XSS"
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

Action not permitted

CVE-2026-26028 (GCVE-0-2026-26028)

FKIE_CVE-2026-26028

GHSA-G2G4-47GV-P72V

Summary

Details

PoC

Impact

Tags

Sightings

Nomenclature