CVE-2025-26210: DeepSeek R1 through V3.1 allows XSS, as demonstrated by JavaScript execution in the context of the run-html-ch

This month

HIGH 8.8DOWNGRADEMITIGATEDOWNGRADE

CVE-2025-26210 is a high-severity flaw (CVSS 8.8) affecting deepseek-r1, deepseek-v2, deepseek-v3. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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.

Why this priority

High severity
Public exploit reference

No fix is published yet: follow the downgrade or mitigation steps.

Risk facts

CVSS score	8.8 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	Required
EPSS exploit chance	0.6% (top 52%)
CISA exploited list	No
Weakness	CWE-79
Published	2025-09-03
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: deepseek

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2025-09-03 14:15 UTCPublished CVE record published
2026-06-17 09:01 UTCUpdated Record last modified

deepseek deepseek-r1 DOWNGRADE

Affected: 1.0

Fixed in: no fixed release known

Safe to downgrade to: a release before 1.0

1. Check installed version

apt-cache policy deepseek-r1 || rpm -q deepseek-r1 || deepseek-r1 --version

2. No fixed release: DOWNGRADE to a release before 1.0 (Debian / Ubuntu)

apt-cache madison deepseek-r1 sudo apt install deepseek-r1=<VERSION_BEFORE_1.0> sudo apt-mark hold deepseek-r1

2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list deepseek-r1 sudo dnf downgrade deepseek-r1-<VERSION_BEFORE_1.0> sudo dnf versionlock add deepseek-r1

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

deepseek deepseek-v2 MITIGATE

Affected: all versions

Fixed in: no fixed release known

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy deepseek-v2 || rpm -q deepseek-v2 || deepseek-v2 --version

No fixed or unaffected release known

Apply the vendor mitigation from the advisory, disable the affected feature, or restrict network access.

deepseek deepseek-v3 DOWNGRADE

Affected: 1.0

Fixed in: no fixed release known

Safe to downgrade to: a release before 1.0

1. Check installed version

apt-cache policy deepseek-v3 || rpm -q deepseek-v3 || deepseek-v3 --version

2. No fixed release: DOWNGRADE to a release before 1.0 (Debian / Ubuntu)

apt-cache madison deepseek-v3 sudo apt install deepseek-v3=<VERSION_BEFORE_1.0> sudo apt-mark hold deepseek-v3

2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list deepseek-v3 sudo dnf downgrade deepseek-v3-<VERSION_BEFORE_1.0> sudo dnf versionlock add deepseek-v3

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2025-26210?

deepseek-r1: downgrade or apply the listed mitigation; deepseek-v2: mitigate or apply the listed mitigation; deepseek-v3: downgrade or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2025-26210 being exploited?

CVE-2025-26210 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2025-26210 affect?

CVE-2025-26210 affects deepseek-r1, deepseek-v2, deepseek-v3. Severity is high (CVSS 8.8). 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.

How urgent is CVE-2025-26210?

Priority 48/100. High severity; Public exploit reference

References

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