DeepSeek V4: Session isolation failure exposes other users' reasoning data
Summary
DeepSeek V4 chat interface at chat.deepseek.com may return reasoning chain content from other users' sessions when a specially crafted input is sent in a new conversation. An unauthenticated remote attacker could obtain parts of other users' conversations, which may include sensitive information entered as context. The public description is limited, the vendor has published no advisory, and the CVSS score of 9.1 is disputed (VulDB: 6.3).
Affected
- DeepSeek V4 chat interface (chat.deepseek.com)
- Affected versions: Unknown.
- Whether the DeepSeek V4 API is affected: Unknown.
Fixed in
- Unknown. A GitHub gist reports the status as 'Fixed by vendor', but no vendor advisory, changelog or fix date was found.
Workaround
- No vendor-published workaround found.
- Do not enter confidential, client or personal data into the public chat interface.
Exploitation
- No known exploitation in the wild. CISA KEV: No.
- A public proof of concept is described in a GitHub gist; its contents were not independently verified. VulDB states no exploit is available.
- CISA SSVC: Exploitation 'poc', automatable: yes, technical impact: total.
Our recommendation
- Treat the public DeepSeek chat service as untrusted for confidential data; block or restrict it where necessary.
- Monitor for shadow AI use and inform staff of the risk.
- If business use is required, review the contract and data processing terms of the API or enterprise offering.
- Watch for a vendor advisory, a confirmed fix date and NVD analysis.
- Priority: moderate for most SMEs; high if staff regularly enter client or personal data into the service.
Public exploits
PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.
Research sources
- CVE-2026-52394 GitHub gist (discoverer write-up) gist.github.com
- VulDB entry for CVE-2026-52394 vuldb.com
- Vulners entry for CVE-2026-52394 vulners.com
- Strix CVE record for CVE-2026-52394 www.strix.ai
- FAR.AI: Security stress test of DeepSeek V4 Pro safeguards www.far.ai
- DeepSeek website (referenced in CVE record) deepseek.com
Researched and written up in English and German by an AI (Claude by Anthropic) based on NVD, CISA, EPSS and the sources listed. The vendor information is authoritative. Researched on 31 Oct 2026, 06:45.
Original description (NVD)
DeepSeek V4 is vulnerable to Incorrect Access Control via a crafted input.
Sources
The tracker combines official, freely usable data sources – updated continuously:
- NVD (NIST) – CVEs, rating (CVSS), affected products
- CISA KEV – vulnerabilities confirmed by CISA as actively exploited
- CISA Vulnrichment – CISA assessment (SSVC) in the official CVE record
- FIRST EPSS – probability of exploitation
- Microsoft MSRC – Patch Tuesday: vulnerabilities, severity, updates
- PoC-in-GitHub – public proof-of-concept repositories
- Metasploit (Rapid7) – modules of the Metasploit Framework
- Exploit-DB (OffSec) – archive of public exploits (links only)
- Patch days: official vendor pages (linked per vendor) (Vendor patch days)
This product uses data from the NVD API but is not endorsed or certified by the NVD. EPSS data © FIRST.org.
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