How severe is CVE-2026-31951?

CVE-2026-31951 has a CVSS 3.x base score of 6.8, rated medium severity. It is exploitable over network with low attack complexity, requires low privileges and user interaction. Impact on confidentiality is high, integrity none, and availability none.

Is CVE-2026-31951 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (15th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2026-31951?

CVE-2026-31951 primarily affects Librechat. In total, 2 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2026-31951?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

Does CVE-2026-31951 have an EU (EUVD) identifier?

Yes. CVE-2026-31951 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-16769.

When was CVE-2026-31951 published?

CVE-2026-31951 was published on 2026-03-27 and last updated on 2026-06-17.

CVE-2026-31951

CVE-2026-31951 is a medium-severity vulnerability in Librechat with a CVSS 3.x base score of 6.8. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-200.

Key facts

Severity: Medium (CVSS 3.x base score 6.8)
EPSS exploit prediction: 0% (15th percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-16769
Weakness: CWE-200
Affected product: Librechat
Published: 2026-03-27
Last modified: 2026-06-17

Description

LibreChat is a ChatGPT clone with additional features. In versions 0.8.2-rc1 through 0.8.3-rc1, user-created MCP (Model Context Protocol) servers can include arbitrary HTTP headers that undergo credential placeholder substitution. An attacker can create a malicious MCP server with headers containing `{{LIBRECHAT_OPENID_ACCESS_TOKEN}}` (and others), causing victims who call tools on that server to have their OAuth tokens exfiltrated. Version 0.8.3-rc2 fixes the issue.

Frequently asked questions

What is CVE-2026-31951?: LibreChat is a ChatGPT clone with additional features. In versions 0.8.2-rc1 through 0.8.3-rc1, user-created MCP (Model Context Protocol) servers can include arbitrary HTTP headers that undergo credential placeholder substitution. An attacker can create a malicious MCP server with headers containing `{{LIBRECHAT_OPENID_ACCESS_TOKEN}}` (and others), causing victims who call tools on that server to have their OAuth tokens exfiltrated. Version 0.8.3-rc2 fixes the issue.
How severe is CVE-2026-31951?: CVE-2026-31951 has a CVSS 3.x base score of 6.8, rated medium severity. It is exploitable over network with low attack complexity, requires low privileges and user interaction. Impact on confidentiality is high, integrity none, and availability none.
Is CVE-2026-31951 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (15th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2026-31951?: CVE-2026-31951 primarily affects Librechat. In total, 2 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2026-31951?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
Does CVE-2026-31951 have an EU (EUVD) identifier?: Yes. CVE-2026-31951 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-16769.
When was CVE-2026-31951 published?: CVE-2026-31951 was published on 2026-03-27 and last updated on 2026-06-17.

References

https://github.com/danny-avila/LibreChat/security/advisories/GHSA-pmw7-gqwj-f954

Affected products (2)

cpe:2.3:a:librechat:librechat:*:*:*:*:*:*:*:*
cpe:2.3:a:librechat:librechat:0.8.3:rc1:*:*:*:*:*:*

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