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PatchSiren cyber security CVE debrief

CVE-2026-40518 bytedance CVE debrief

CVE-2026-40518 is a HIGH severity vulnerability in Bytedance DeerFlow before commit 2176b2b. It allows for path traversal and arbitrary file write via bootstrap-mode custom-agent creation. The vulnerability exists due to a bypass in agent name validation, enabling attackers to supply traversal-style values or absolute paths as the agent name. This can influence directory creation and write files outside the intended custom-agent directory, potentially achieving arbitrary file write on the system subject to filesystem permissions.

Vendor
bytedance
Product
deer-flow
CVSS
HIGH 7.1
CISA KEV
Not listed in stored evidence
Original CVE published
2026-04-17
Original CVE updated
2026-07-14
Advisory published
2026-04-17
Advisory updated
2026-07-14

Who should care

Users of Bytedance DeerFlow before commit 2176b2b should apply the patch to prevent potential path traversal and arbitrary file write attacks.

Technical summary

The vulnerability has a CVSS score of 7.1 and is classified as HIGH severity. It was published on 2026-04-17T17:17:09.543Z and last modified on 2026-06-05T18:07:07.207Z. The CWE associated with this vulnerability is CWE-22.

Defensive priority

HIGH

Recommended defensive actions

  • Apply the patch referenced at resourceLinkAnnotations ref-4 to update Bytedance DeerFlow to commit 2176b2b or later.
  • Review and follow the issue tracking and patch information at resourceLinkAnnotations ref-5.
  • Refer to the third-party advisory at resourceLinkAnnotations ref-6 for additional information.

Evidence notes

The information provided is based on data from official sources, including CVE.org and the National Vulnerability Database (NVD).

Sources and references

Verified primary and authoritative sources

  • CVE-2026-40518 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-40518

    CVE Program - Official CVE Program record with source-provided CVE metadata.

  • CVE-2026-40518 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-40518

    NIST National Vulnerability Database - Official NIST NVD detail page and source-specific vulnerability assessment.

Supplemental references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.