Vulnerability-Lookup

CVE-2026-70492 (GCVE-0-2026-70492)

Vulnerability from cvelistv5 – Published: 2026-08-04 20:53 – Updated: 2026-08-05 14:41

Title

Open WebUI: Stored XSS via unescaped KaTeX render-error fallback in rendered messages

Summary

Open WebUI is an extensible, feature-rich, and user-friendly self-hosted AI platform. From 0.10.0 until 0.11.0, src/lib/components/chat/Messages/Markdown/KatexRenderer.svelte could store and render a chat message whose math block makes KaTeX fail with a stack overflow instead of a parse error. The catch branch fell back to inserting the original math source into the page as HTML through {@html} rather than as text, so script in the message runs in the browser of whoever views it, including shared chats and channels. The viewer's session token in localStorage can be stolen, and an administrator viewer can have their account taken over. This issue is fixed in 0.11.0.

Severity

8.7 (High)


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

SSVC

Exploitation: poc Automatable: no Technical Impact: partial

CISA Coordinator (v2.0.3)

CWE

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

Assigner

GitHub_M

References

4 references

URL	Tags
https://github.com/open-webui/open-webui/security…	x_refsource_CONFIRM
https://github.com/open-webui/open-webui/pull/26718	x_refsource_MISC
https://github.com/open-webui/open-webui/commit/b…	x_refsource_MISC
https://github.com/open-webui/open-webui/releases…	x_refsource_MISC

Impacted products

1 product

Vendor	Product	Version
open-webui	open-webui	Affected: >= 0.10.0, < 0.11.0

Show details on NVD website

JSON

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GHSA-PWXH-7358-JQ2X

Vulnerability from github – Published: 2026-08-04 20:54 – Updated: 2026-08-04 20:54

Summary

Open WebUI: Stored XSS via unescaped KaTeX render-error fallback in rendered messages

Details

Summary

Any authenticated user can store a chat message whose math block makes KaTeX fail with a stack overflow instead of a parse error. When that happens the renderer falls back to inserting the original math source into the page as HTML rather than as text, so script in the message runs in the browser of whoever views it. Every surface that renders messages is affected, including shared chats and channels, and the missing control is output escaping on the error path.

Preconditions

Default configuration, no flags involved. The attacker needs a normal user account and a way to get the target to open the content: a shared chat link, a channel the target reads, or any other message surface. No admin rights and no non-default settings are required on either side.

Impact

Script executes in the viewer's browser on the Open WebUI origin, which puts the session token in localStorage within reach and therefore allows taking over the viewing account. If the viewer is an administrator, that is administrator access to the instance. Exploitation needs the target to open the content, but nothing beyond that: no interaction with the message itself. Server-side data and availability are unaffected; the impact is entirely in the viewer's browser session.

Fix

Fixed in 0.11.0 by commit bc600d3f0 (PR #26718). The error path now HTML-escapes the math source before it reaches the DOM, so a failed render displays the formula as text instead of as markup. Upgrading fully resolves the issue; no configuration change is needed.

Root cause

Affected component: src/lib/components/chat/Messages/Markdown/KatexRenderer.svelte, the reactive block that renders math and its catch branch. Affected setup: releases 0.10.0 through 0.10.2, which are the versions carrying that fallback.

KaTeX was called with throwOnError: false, which suppresses parse errors but not a RangeError from deeply nested input. The surrounding catch treated any failure as "show the original formula" and assigned the untouched source to the value that the template inserts with {@html}. Because the Markdown math tokenizer captures everything between the delimiters verbatim, including angle brackets and complete tags, the attacker controls that string exactly.

Proof of concept

Send a chat message (or store one via any endpoint that writes message content) consisting of a single inline math block: an opening $, 100000 { characters, an <img src=x onerror=alert(document.domain)> tag, 100000 } characters, and a closing $.

python3 -c 'N=100000; print("$"+"{"*N+"<img src=x onerror=alert(document.domain)>"+"}"*N+"$")'

Open the chat as any user who can view it. KaTeX overflows the stack, the fallback inserts the raw source, and the onerror handler fires. Replacing alert() with a request carrying localStorage.token sends the viewer's session token to an attacker-controlled host; this was demonstrated against a shared chat opened by an administrator account.

Credits

@maxntv — reported the unescaped KaTeX error fallback and demonstrated session-token theft through a shared chat.

Severity

8.7 (High)


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

Show details on source website

JSON

To clipboard

{
  "affected": [
    {
      "package": {
        "ecosystem": "PyPI",
        "name": "open-webui"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0.10.0"
            },
            {
              "fixed": "0.11.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-70492"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-79"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-08-04T20:54:17Z",
    "nvd_published_at": null,
    "severity": "HIGH"
  },
  "details": "## Summary\nAny authenticated user can store a chat message whose math block makes KaTeX fail with a stack overflow instead of a parse error. When that happens the renderer falls back to inserting the original math source into the page as HTML rather than as text, so script in the message runs in the browser of whoever views it. Every surface that renders messages is affected, including shared chats and channels, and the missing control is output escaping on the error path.\n\n## Preconditions\nDefault configuration, no flags involved. The attacker needs a normal user account and a way to get the target to open the content: a shared chat link, a channel the target reads, or any other message surface. No admin rights and no non-default settings are required on either side.\n\n## Impact\nScript executes in the viewer\u0027s browser on the Open WebUI origin, which puts the session token in localStorage within reach and therefore allows taking over the viewing account. If the viewer is an administrator, that is administrator access to the instance. Exploitation needs the target to open the content, but nothing beyond that: no interaction with the message itself. Server-side data and availability are unaffected; the impact is entirely in the viewer\u0027s browser session.\n\n## Fix\nFixed in 0.11.0 by commit bc600d3f0 (PR #26718). The error path now HTML-escapes the math source before it reaches the DOM, so a failed render displays the formula as text instead of as markup. Upgrading fully resolves the issue; no configuration change is needed.\n\n## Root cause\nAffected component: `src/lib/components/chat/Messages/Markdown/KatexRenderer.svelte`, the reactive block that renders math and its `catch` branch. Affected setup: releases 0.10.0 through 0.10.2, which are the versions carrying that fallback.\n\nKaTeX was called with `throwOnError: false`, which suppresses parse errors but not a `RangeError` from deeply nested input. The surrounding `catch` treated any failure as \"show the original formula\" and assigned the untouched source to the value that the template inserts with `{@html}`. Because the Markdown math tokenizer captures everything between the delimiters verbatim, including angle brackets and complete tags, the attacker controls that string exactly.\n\n## Proof of concept\nSend a chat message (or store one via any endpoint that writes message content) consisting of a single inline math block: an opening `$`, 100000 `{` characters, an `\u003cimg src=x onerror=alert(document.domain)\u003e` tag, 100000 `}` characters, and a closing `$`.\n\n```\npython3 -c \u0027N=100000; print(\"$\"+\"{\"*N+\"\u003cimg src=x onerror=alert(document.domain)\u003e\"+\"}\"*N+\"$\")\u0027\n```\n\nOpen the chat as any user who can view it. KaTeX overflows the stack, the fallback inserts the raw source, and the `onerror` handler fires. Replacing `alert()` with a request carrying `localStorage.token` sends the viewer\u0027s session token to an attacker-controlled host; this was demonstrated against a shared chat opened by an administrator account.\n\n## Credits\n@maxntv \u2014 reported the unescaped KaTeX error fallback and demonstrated session-token theft through a shared chat.",
  "id": "GHSA-pwxh-7358-jq2x",
  "modified": "2026-08-04T20:54:17Z",
  "published": "2026-08-04T20:54:17Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/open-webui/open-webui/security/advisories/GHSA-pwxh-7358-jq2x"
    },
    {
      "type": "WEB",
      "url": "https://github.com/open-webui/open-webui/pull/26718"
    },
    {
      "type": "WEB",
      "url": "https://github.com/open-webui/open-webui/commit/bc600d3f085802c45aa8f38c30e6e8c986bde6cc"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/open-webui/open-webui"
    },
    {
      "type": "WEB",
      "url": "https://github.com/open-webui/open-webui/releases/tag/v0.11.0"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Open WebUI: Stored XSS via unescaped KaTeX render-error fallback in rendered messages"
}

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.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.

Action not permitted

CVE-2026-70492 (GCVE-0-2026-70492)

GHSA-PWXH-7358-JQ2X

Summary

Preconditions

Impact

Fix

Root cause

Proof of concept

Credits

Tags

Sightings

Nomenclature