BISHENG: Directory traversal in knowledge upload via filename
Summary
BISHENG versions 2.3.0, 2.4.0 and 2.4.0-beta1 contain a directory traversal flaw in the save_download_file function. The uploaded filename is not sanitized, so a crafted name with ../ sequences can place files outside the intended cache folder. Public reports describe the knowledgeUpload API endpoint as the entry point, and an attacker with network access may be able to write arbitrary files on the host, which could lead to code execution or data tampering.
Affected
- BISHENG 2.3.0
- BISHENG 2.4.0
- BISHENG 2.4.0-beta1
- The upstream issue #1994 lists the latest version as of 2026-04-20 as affected; the exact range is unconfirmed.
Fixed in
Unknown. No vendor advisory or release note naming a fixed version was found.
Workaround
- Restrict network access to BISHENG and do not expose it directly to the internet; use VPN or SSO.
- Run the BISHENG service with least privileges and limit its write access to its own data directories.
- Review upload logs for filenames containing path separators or parent-directory references.
- Limit which accounts can use the upload functions.
Exploitation
- A public gist with reproduction notes exists; its content was not reviewed.
- SSVC assessment: exploitation PoC, automatable: yes, technical impact: total.
- Not listed in CISA KEV according to one secondary source; verify on cisa.gov.
- Exploitation in the wild: Unknown.
Our recommendation
- Inventory all BISHENG 2.3.x and 2.4.0 instances, including Docker deployments.
- Remove direct internet exposure and enforce SSO or VPN access.
- Apply a vendor fix as soon as it is confirmed on the dataelement/bisheng releases page.
- Apply the workarounds above until then and monitor the NVD and the GitHub issue for updates.
Public exploits
PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.
Research sources
- CVE-2026-51859 gist (Ro1ME) gist.github.com
- GitHub issue #1994 dataelement/bisheng github.com
- VulnCheck/Vulnrichment CVE-2026-51859 vulners.com
- VulDB CVE-2026-51859 vuldb.com
- BISHENG GitHub repository github.com
- BISHENG releases github.com
- GitHub issue #1993 dataelement/bisheng github.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, 07:50.
Original description (NVD)
bisheng 2.3.0, 2.4.0, and 2.4.0-beta1 is vulnerable to directory traversal in save_download_file (src/backend/bisheng/core/cache/utils.py:290).
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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