CVE-2026-81213

Executive Summary

CVE-2026-81213 is a Server-Side Request Forgery (SSRF) vulnerability (CWE-918) in IBM Langflow OSS versions 1.0.0 through 1.11.5, caused by improper validation of user-supplied URLs. A remote, unauthenticated attacker can cause the Langflow server to issue requests to internal network resources, enabling retrieval of sensitive information from systems not normally reachable from the internet. With a CVSS base score of 8.6 (High), a scope change (S:C), and high confidentiality impact under no authentication requirement, this is a serious exposure for any internet-facing Langflow deployment.

Technical Analysis

The vulnerability class is server-side request forgery. Langflow is a low-code visual framework for building LLM and agentic applications, which routinely fetches remote content — for example, loading data from URLs, pulling remote specifications, or connecting to external services configured through the UI or API. CVE-2026-81213 arises because the product performs "improper validation of user-supplied URLs," meaning a URL supplied by a user to such a fetch component is not adequately constrained before the server itself makes the outbound request.

In SSRF, the server acts as an unwitting proxy: the attacker does not need direct routing to the target internal asset; the Langflow process does the fetching on their behalf. Because the request originates from the Langflow host, it can reach resources that are protected by network topology — loopback services, RFC1918 private ranges, and internal-only HTTP endpoints. The absence of proper URL validation typically permits one or more of: non-HTTP schemes, loopback and private-range destinations, redirect chains that pivot to internal hosts, or URLs whose host component resolves to an internal address (DNS rebinding/TOCTOU patterns). The NVD description does not enumerate the specific parsing routines, parameter names, or endpoints involved, and it would be inaccurate to invent them; what is derivable is that user-controlled URL input reaches an outbound-fetch path without sufficient validation.

The CVSS vector CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:N/A:N is highly informative. Network attack vector and low attack complexity indicate the flaw is reachable remotely with no special conditions. PR:N/UI:N means no authentication and no user interaction are required — the attacker only needs network reachability to the Langflow instance. The scope change (S:C) reflects that the vulnerable Langflow component is leveraged to impact resources beyond its own security authority — specifically, other internal systems reachable from it. Confidentiality is High (C:H) because internal response bodies can be exfiltrated; integrity and availability are None (I:N/A:N), so there is no direct data modification or denial of service from the flaw itself. The overall score of 8.6 is therefore an information-disclosure SSRF rather than a code-execution or destructive primitive, though its pivot value is significant.

Note on product naming: the CNA title field is empty and the NVD description attributes the product to "IBM Langflow OSS." Langflow is an open-source project associated with DataStax/IBM; the version range cited (1.0.0 through 1.11.5) is the authoritative affected scope from the advisory data. There is no public exploit code or Nuclei template associated with this record, despite a PoC status of "Public" — treat detection engineering as behavioral rather than signature-based.

Exploitation Scenarios

The following chain is described at the vulnerability-class level, consistent with the NVD description. No public PoC is available; the attacker steps below are inferred from the SSRF class and should not be read as confirmed implementation details.

1. Reconnaissance / target identification. The attacker identifies an exposed Langflow instance. Langflow is commonly served on its default web port (historically 7860), and internet-wide scans can enumerate it via HTTP title/body fingerprints. The attacker confirms the instance is reachable and that unauthenticated or low-privilege access to the URL-accepting functionality is possible (CVSS PR:N/UI:N indicates auth is not required).

2. Triggering the flaw. The attacker supplies a crafted URL to a feature that causes Langflow to fetch server-side content. Because validation of the user-supplied URL is improper, the attacker directs the request inward — for example, toward loopback (127.0.0.1/::1), RFC1918 private ranges (10.0.0.0/8, 172.16.0.0/12, 192.168.0.0/16), or internal hostnames only resolvable from the Langflow network. The exact endpoints and parameters are not disclosed in the advisory; the mechanism is that the server's outbound HTTP client performs the request on the attacker's behalf.

3. Payload / execution method (class level). The "payload" is a URL pointing at an internal resource. Variants that defeat naive filtering include alternate IP encodings, non-canonical host forms, and redirect-based pivots where an attacker-controlled URL returns an HTTP redirect to an internal address. The response from the internal resource is returned to or observable by the attacker through the Langflow feature's normal output.

4. Post-exploitation impact. Successful SSRF yields confidential data from internal systems — internal web services, admin panels, metadata services, or APIs that do not require authentication but are network-isolated. This is a reconnaissance and pivot primitive: C:H with S:C means the attacker can read sensitive internal content and use that access to map the internal environment and stage further attacks. There is no direct integrity or availability impact from the flaw itself.

Impact Assessment

Business impact centers on unauthorized disclosure of internal data and internal-network reconnaissance. Any organisation running Langflow 1.0.0–1.11.5 on an internet-reachable or broadly reachable interface is in scope; deployments where Langflow sits inside a trusted network segment (elastic compute, Kubernetes clusters, CI runners, internal data fabrics) face an elevated blast radius because the SSRF pivot executes from that trusted position.

Mapping to CVSS subscores: AV:N and AC:L mean exploitation is remote and trivial once the service is reachable; PR:N/UI:N mean no credentials or victim action are needed; S:C captures that other internal systems are impacted through the Langflow host; C:H is the core impact — internal secrets, configuration, and service responses can be read; I:N/A:N means no direct tampering or outage. EPSS is 0.00355 (29th percentile), indicating low near-term mass-exploitation likelihood as of the data provided, and the CVE is not in CISA KEV. However, SSRF vulnerabilities in AI/agent tooling are attractive for reconnaissance because the surrounding infrastructure (cloud metadata endpoints, internal model gateways, vector databases) is often highly sensitive. Blast radius depends entirely on what the Langflow host can reach.

Detection Guidance

Sigma Rule

title: Potential SSRF in Langflow via User-Supplied URL
id: 8b6c1e2a-4f3d-4c9b-9f21-7a1d2e5c8b90
status: experimental
description: Detects Langflow server-side processes issuing requests to internal/loopback destinations, consistent with CVE-2026-81213 SSRF.
references:
  - https://nvd.nist.gov/vuln/detail/CVE-2026-81213
author: valtersit.com
date: 2026/01/01
logsource:
  category: network_connection
  product: linux
detection:
  selection_proc:
    Image|endswith:
      - '/python'
      - '/python3'
      - '/langflow'
  selection_dst:
    DestinationIp|cidr:
      - '127.0.0.0/8'
      - '10.0.0.0/8'
      - '172.16.0.0/12'
      - '192.168.0.0/16'
      - '169.254.0.0/16'
  condition: selection_proc and selection_dst
falsepositives:
  - Legitimate Langflow components that intentionally talk to internal services
level: medium
tags:
  - attack.t1190
  - cve.2026.81213

YARA Rule

rule CVE_2026_81213_Langflow_SSRF_URL
{
    meta:
        description = "Detects SSRF-style internal-target URLs in Langflow request/config content (CVE-2026-81213)"
        author = "valtersit.com"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2026-81213"
        date = "2026-01-01"
        severity = "high"

    strings:
        $p1 = "http://127.0.0.1"
        $p2 = "http://localhost"
        $p3 = "http://0.0.0.0"
        $p4 = "http://169.254.169.254"
        $p5 = "http://[::1]"
        $r1 = "http://10."
        $r2 = "http://192.168."
        $r3 = "http://172.16."
        $r4 = "http://172.17."
        $r5 = "http://172.18."
        $intent = "url"

    condition:
        $intent and any of ($p*) or 2 of ($r*)
}

Suricata IDS Rule

alert http $HOME_NET any -> $HOME_NET any (msg:"CVE-2026-81213 Langflow SSRF - Internal Target URL in Request"; flow:to_server,established; http.method; content:"GET"; http.uri; pcre:"/(http(s)?|file|gopher|dict):\/\/(127\.0\.0\.1|localhost|0\.0\.0\.0|169\.254\.169\.254|10\.|192\.168\.|172\.(1[6-9]|2[0-9]|3[01])\.)/i"; reference:cve,2026-81213; reference:url,nvd.nist.gov/vuln/detail/CVE-2026-81213; classtype:attempted-recon; sid:202681213; rev:1;)

Elastic Detection

query: >
  network where
    process.name in ("python", "python3", "langflow")
    and destination.ip != null
    and (cidrMatch(destination.ip, "127.0.0.0/8") or
         cidrMatch(destination.ip, "10.0.0.0/8") or
         cidrMatch(destination.ip, "172.16.0.0/12") or
         cidrMatch(destination.ip, "192.168.0.0/16") or
         cidrMatch(destination.ip, "169.254.0.0/16"))

Splunk SPL Query

index=network sourcetype=pan:traffic OR sourcetype=zeek:conn
| eval internal=if(cidrmatch("10.0.0.0/8",dest_ip) OR cidrmatch("172.16.0.0/12",dest_ip) OR cidrmatch("192.168.0.0/16",dest_ip) OR cidrmatch("127.0.0.0/8",dest_ip) OR cidrmatch("169.254.0.0/16",dest_ip),1,0)
| where internal=1 AND match(lower(process_name),"langflow|python")
| stats count values(dest_ip) as internal_targets by src_ip, process_name
| where count > 10

Wazuh OSSEC Rule

<group name="langflow,ssrf,cve-2026-81213,">
  <rule id="2026813" level="10">
    <if_sid>5710</if_sid>
    <field name="dstip">^127\.|^10\.|^192\.168\.|^172\.(1[6-9]|2[0-9]|3[01])\.|^169\.254\.</field>
    <description>CVE-2026-81213: Langflow process contacted an internal/loopback address (possible SSRF)</description>
    <mitre>
      <id>T1190</id>
    </mitre>
    <group>cve_2026_81213,</group>
  </rule>
</group>

Mitigation & Patch Guidance

Patch confidence: 2/4 (CLAIMED — single source claims patch; not independently confirmed). The NVD record states a fix is available, but no vendor advisory, fixed-version identifier, or commit reference is provided in the data supplied. Treat the patch status as unverified.

1. Immediate mitigations (apply even before patching):

• Remove Langflow from direct internet exposure. Place it behind an authenticating reverse proxy and restrict network access to trusted operators only.
• Egress filtering: block outbound traffic from the Langflow host to loopback, RFC1918 ranges, and the cloud metadata address (169.254.169.254) using host firewall or network policy. This neutralises the SSRF pivot regardless of input validation.
• Enforce IMDSv2 / disable instance metadata access where feasible, and segment AI-tooling hosts from sensitive internal services.
• Audit recent Langflow request logs for outbound fetches to internal destinations to determine whether the flaw has already been exercised.

2. Patch / upgrade steps:

• Apply the fix claimed available for this CVE once the vendor publishes the specific fixed version and advisory. Because the affected range is cited as 1.0.0 through 1.11.5, plan an upgrade to the first version explicitly documented by the maintainer as remediated.
• Verify the patch by confirming that user-supplied URLs are validated against an allowlist and that non-HTTP schemes, private/loopback addresses, and redirect-based pivots are rejected.
• Do not rely solely on the NVD "patch available" claim; validate against the upstream Langflow release notes/security advisory.

3. Long-term hardening:

• Adopt allowlist-based egress (deny-by-default) for application servers, especially agent/LLM platforms that fetch remote content.
• Treat all URL-fetch features as untrusted input paths; require scheme, host, and resolved-IP validation with re-validation after redirects (defeat DNS rebinding/TOCTOU).
• Deploy SSRF-aware network controls (proxy with URL filtering) in front of outbound fetch functionality.
• Continuously monitor for T1190 behaviour and maintain inventory of internet-facing Langflow instances.

References

• NVD — CVE-2026-81213: https://nvd.nist.gov/vuln/detail/CVE-2026-81213
• CWE-918 Server-Side Request Forgery: https://cwe.mitre.org/data/definitions/918.html
• MITRE ATT&CK T1190 — Exploit Public-Facing Application: https://attack.mitre.org/techniques/T1190/
• OWASP — Server-Side Request Forgery: https://owasp.org/www-community/attacks/Server_Side_Request_Forgery
• CISA Known Exploited Vulnerabilities Catalog (check for update; CVE-2026-81213 not listed as of this data): https://www.cisa.gov/known-exploited-vulnerabilities-catalog

Threat actor / exploit-in-the-wild note: No CISA KEV listing, no associated exploit code, and no named threat-actor campaign are present in the provided intelligence. EPSS is 0.00355 (29th percentile), indicating low observed exploitation probability. PoC status is "Public," suggesting public research or disclosure exists, but this must not be conflated with working exploit code — none is confirmed in the supplied data.