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MEDIUM severity

CVE-2026-46678 — pydantic-ai

MEDIUM

CVE-2026-46678 is a medium-severity (CVSS 6.8) Server-Side Request Forgery (SSRF) vulnerability in pydantic-ai. A fix is available for pydantic-ai — see the affected versions and patch details below.

Pydantic AI: SSRF cloud-metadata blocklist bypass via IPv4-mapped IPv6 (Incomplete fix of CVE-2026-25580)

Also known asGHSA-cqp8-fcvh-x7r3PYSEC-2026-2978PYSEC-2026-2982
Published
Jul 29, 2026
Updated
Aug 12, 2026
Affected
2 pkgs
Patched
2 / 2
Exploits
None indexed
Exploitation data as of Sep 30, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

  • CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-46678.

EPSS Exploitation Probability

via FIRST.org ↗
0.4%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs30th percentile — riskier than 30% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

CVE-2026-46678 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 381,682 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.

Real-World Exposure

2 pkgs affected
🐍pydantic-ai🐍pydantic-ai-slim

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.

Description

Summary

When an application using Pydantic AI opts a URL into force_download='allow-local' (which disables the default block on private/internal IPs), the cloud-metadata blocklist could be bypassed by encoding the metadata IP in an IPv6 transition form (IPv4-mapped IPv6, 6to4, or NAT64). Dual-stack and translated networks route the IPv6 wrapper to the underlying IPv4 endpoint, exposing cloud IAM short-term credentials.

This is an incomplete fix of GHSA-2jrp-274c-jhv3 / CVE-2026-25580. The parent advisory's remediation guaranteed that "cloud metadata endpoints are always blocked, even with allow-local." That guarantee did not hold for IPv6-encoded forms of the metadata IPs.

Severity

Same impact metrics as the parent CVE, but materially narrower attack surface (AC:H instead of AC:L), because exploitation requires the application to have opted into allow-local on a URL influenced by untrusted input.

Who Is Affected

Applications are affected only if they explicitly opt for FileUrl (ImageUrl, AudioUrl, VideoUrl, DocumentUrl) into force_download='allow-local' on a URL that is, or could be, influenced by untrusted input.

Applications are not affected if they use any of the bundled integrations to ingest user input, because they do not propagate force_download from external data:

  • Agent.to_web / clai web
  • VercelAIAdapter
  • AGUIAdapter / Agent.to_ag_ui

Applications that only download from developer-controlled URLs are not affected.

Remediation

Upgrade to 1.99.0 or later. The cloud-metadata and private-IP blocklists now apply to IPv6 transition forms that route to a blocked IPv4 endpoint (IPv4-mapped IPv6, 6to4, and NAT64 well-known prefix). The blocklists have also been extended to cover additional IANA-reserved IPv4 and IPv6 special-purpose ranges.

Workaround for Unpatched Versions

Avoid passing force_download='allow-local' on any URL that could be influenced by untrusted input. If developers must, resolve the hostname themselves and validate the result against their own metadata blocklist — including IPv6-encoded forms — before constructing the FileUrl.

Credits

Reported by j0hndo.

Affected Packages

2 total 2 fixed
EcosystemPackageVulnerable rangeFix
🐍PyPIpydantic-ai≥ 1.56.0&&< 1.99.01.99.0pip install --upgrade 'pydantic-ai==1.99.0'
🐍PyPIpydantic-ai-slim≥ 1.56.0&&< 1.99.01.99.0pip install --upgrade 'pydantic-ai-slim==1.99.0'

Affected Products

1 product · 1 configurations
Application
pydantic aipydantic
≥ 1.56.0 && < 1.99.0
range

Detection & mitigation playbook

Open-source dependency

  1. Detect

    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for pydantic-ai, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

  2. Fix

    Update pydantic-ai to 1.99.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-46678 is resolved across your whole dependency graph.

  3. Workarounds

    Restrict outbound requests from the affected component to an allowlist of hosts, block access to link-local and internal address ranges at the network layer, and require authentication on internal services so a forged request cannot reach them unauthenticated.

Frequently Asked Questions

## Summary When an application using Pydantic AI opts a URL into `force_download='allow-local'` (which disables the default block on private/internal IPs), the cloud-metadata blocklist could be bypassed by encoding the metadata IP in an IPv6 transition form (IPv4-mapped IPv6, 6to4, or NAT64). Dual-stack and translated networks route the IPv6 wrapper to the underlying IPv4 endpoint, exposing cloud IAM short-term credentials. This is an incomplete fix of [GHSA-2jrp-274c-jhv3](https://github.com/pydantic/pydantic-ai/security/advisories/GHSA-2jrp-274c-jhv3) / [CVE-2026-25580](https://nvd.nist.go
O3 Security · Impact-Aware SCA

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CVE-2026-46678: pydantic-ai — Fixed in 1.99.0 | O3 Security