HighVulnerability

CVE-2026-31943: LibreChat SSRF protection bypass via IPv4-mapped IPv6 addresses

Source: NVD(opens in a new tab)
Identifier: CVE-2026-31943
Published: March 27, 2026
Record updated: October 9, 2026

Known exploitation: Not listed in the CISA Known Exploited Vulnerabilities catalog at the last check.
EPSS: 0.2%

Summary

CVE-2026-31943 affects LibreChat before version 0.8.3. The function `isPrivateIP()` in `packages/api/src/auth/domain.ts` fails to detect IPv4-mapped IPv6 addresses in hex-normalized form. Any authenticated user can exploit this to bypass SSRF protection and make the server send HTTP requests to internal resources, including cloud metadata services such as `169.254.169.254`, loopback, and RFC1918 ranges.

Mitigation

Fixed in 0.8.3.

Details

Scores and exploitation

CVSS score: 8.5(high)
CVSS vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:L/A:N
Attack vector: network
Attack complexity: low
Privileges required: low
User interaction: none
EPSS: 0.2%Estimated probability that this CVE is exploited in the next 30 days, from the FIRST Exploit Prediction Scoring System. Read on November 8, 2026.
Disclosure date: March 27, 2026

Weaknesses and techniques

Weakness (CWE): CWE-918
Attack pattern (CAPEC): CAPEC-664

Classification

Attack type: Other
Attack sophistication: Moderate
AI component targeted: API
Impact: Confidentiality,
Integrity
Labels: security

How this record was produced

Summaries, mitigations and labels on this page are generated automatically from the source. The linked source is authoritative. The source gives this advisory a description and no title, so the title above is a headline generated from the source text.

Original source: https://nvd.nist.gov/vuln/detail/CVE-2026-31943

First tracked: March 28, 2026 at 02:07 AM ET, from NVD/CVE Database

Classifier: claude-haiku-5-5, prompt v4

Classifier confidence: 85% (self-assessed)

Summary

Mitigation

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