DeepSeek R1 through V3.1 allows XSS, as demonstrated by JavaScript execution in the context of the run-html-chat.deepseeksvc.com domain.

published 2025-09-03 14 mo ago modified 2026-06-17 4 mo ago also EUVD-2025-26507

cvss: 8.8; version 3.1, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 0.6%; EPSS 0.6% chance of exploitation in 30 days, percentile 49%
public exploits: 0; none known

DeepSeek R1 through V3.1 allows XSS, as demonstrated by JavaScript execution in the context of the run-html-chat.deepseeksvc.com domain. NOTE: some third parties have indicated that this is intended behavior.

CISA SSVC

Exploitation: Proof of concept is public
Automatable: no
Technical impact: total
Assessed: 14 mo ago (2025-09-08)

Exploit prediction

0.60% chance of exploitation in the next 30 days, higher than 49% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

hackmd.io https://hackmd.io/@MrqrFIlhQFi7vUwkqbrXDw/deepseek referenced PoC, tagged "exploit" by a source, unverified
youtu.be https://youtu.be/IgQwy52FVT4 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by	version	score	vector
CISA ADP	3.1	8.8	CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
CNA	3.1	8.8	CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H

Classification

Weakness

CWE-79 Improper Neutralization of Input During Web Page Generation

References

hackmd.io /@MrqrFIlhQFi7vUwkqbrXDw/deepseek
exploit, third-party-advisory
youtu.be /IgQwy52FVT4
exploit
deepseek.com
permissions-required

Sources

CVE List CVE-2025-26210
NVD CVE-2025-26210

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

Summary