Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata – not a confirmed exploit chain
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AccessInduce Negotiate-authenticated curl to attacker-influenced URL
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ExploitServer returns redirect to foreign origin
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Executioncurl resends Negotiate credentials cross-origin
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ImpactAttacker captures leaked GSS-API/Kerberos token
Vulnerability Assessment
| Exploitation Conditions | Requires a client built and invoked to use Negotiate (GSS-API/SPNEGO/Kerberos) HTTP authentication AND configured to follow redirects (e.g. -L / CURLOPT_FOLLOWLOCATION), running an affected version (curl/libcurl 8.21.0 through 8.22.0). Exploitation is triggered when the originally-contacted server issues an HTTP redirect to a different origin, at which point curl incorrectly forwards the Negotiate credentials to that redirected origin. LIMITING FACTORS: Negotiate auth is not a default mode and is used in a minority of enterprise Kerberos/SSO deployments; the attacker must control or influence either the initial server's redirect response or the redirect destination; impact is limited to exposure of the authentication token to an unintended origin rather than direct code execution or data modification. |
| Impact | No quantitative risk signals are available: CVSS score and vector are N/A, there is no EPSS probability, no CISA KEV listing, and no public exploit code is referenced. The only authoritative signal is the curl project's own severity rating of LOW for CVE-2026-86413 ('Negotiate credentials sent to redirected origin'), published alongside the curl 8.23.0 release on 2026-10-14. Because the CVSS vector is missing, authentication and attack-vector qualifiers cannot be confirmed from input data. The real-world priority is low: exploitation is contingent on a narrow, non-default usage pattern (a client explicitly using Negotiate/GSS-API authentication that then follows a cross-origin redirect), rather than a broadly automatable network attack. This should be treated as a credential-hygiene defect to patch during normal maintenance, not an emergency - there is no evidence of active exploitation and no POC identified at time of analysis. Note the tension between the product's enormous footprint and the flaw's low severity: curl is ubiquitous, but this specific weakness affects only a small fraction of configurations. |
| Exploit ScenarioDerived | A user or automated job runs curl/libcurl with Negotiate (Kerberos/SPNEGO/GSS-API) authentication and redirect-following enabled against a server the attacker controls or can influence. The server returns an HTTP redirect to a foreign origin, and curl improperly sends the Negotiate credentials (authentication token) to that redirected origin, leaking them to a host that should not receive them. No public exploit code is identified at time of analysis. |
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Alert meAnalysisAIv1 – Oct 14, 2026
Negotiate (Kerberos/SPNEGO) credentials are forwarded to the wrong origin by curl and libcurl 8.21.0 through 8.22.0 when the initially contacted server returns an HTTP redirect to a different host while redirect following is enabled. An attacker who controls or influences either the redirect response or the redirect destination can capture the Negotiate authentication token, resulting in limited confidentiality exposure rather than code execution or data modification. The flaw is rated LOW by the curl project, no public exploit code has been identified at time of analysis, and it was fixed in the curl 8.23.0 release published on 2026-10-14 alongside twenty-three other advisories.
RemediationAI
Upgrade to curl/libcurl 8.23.0, the release that contains the fix for this and the other twenty-three advisories published on 2026-10-14; the curl project's security page at https://curl.se/docs/security.html lists each CVE with a link to the fixing commit, and the oss-security announcement is at https://seclists.org/oss-sec/2026/q4/154 (commercial LTS builds are available via https://rock-solid.curl.dev, which applies only security and stability patches to long-term branches). Where upgrading cannot be done immediately, the most effective compensating control is to stop following redirects in any session that uses Negotiate authentication: remove -L / --location from the curl invocation, or unset CURLOPT_FOLLOWLOCATION in libcurl, and instead resolve and validate redirect targets out-of-band before issuing a second request. The trade-off is that legitimate redirect-driven workflows (login flows, load-balanced endpoints, captive portals) will break or require re-implementation, and callers must ensure they do not substitute --location-trusted, which deliberately forwards credentials to other hosts and would defeat the mitigation. Additional optionally layered controls include restricting Negotiate to explicitly allow-listed origins, using a dedicated credential cache with short ticket lifetimes to limit the usefulness of any leaked token, and confining outbound traffic to vetted proxy or egress paths so an attacker cannot easily steer a redirect to an attacker-controlled Negotiate-accepting endpoint.
Affected ProductsAI
curl and libcurl versions 8.21.0 through 8.22.0 are affected (the vulnerability was introduced in 8.21.0 per the curl vulnerability table and fixed in 8.23.0). The CVE record supplied here contains no CPE strings and no CVSS vector or score, so affected scope must be determined from the curl project's own version table at https://curl.se/docs/security.html and the advisory thread at https://seclists.org/oss-sec/2026/q4/154. Any application embedding libcurl in this version range, or any deployment of the curl command-line tool in this range, is potentially impacted if it uses Negotiate authentication; because libcurl is statically or dynamically bundled into a very large number of downstream products (the project cites more than twenty billion installations across appliances, embedded devices, and applications), downstream distributors must map this back to their bundled curl version.
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Technical ContextAI · show details
Negotiate is the GSS-API/SPNEGO-based HTTP authentication mechanism (RFC 4559) that lets a client present a Kerberos ticket to a server, and it is typically deployed inside enterprise SSO/Kerberos environments rather than by default. The root cause class is improper handling of authentication state across origin boundaries during redirect processing: curl tracks credential scope and connection/authentication state internally, and in the affected versions that state did not correctly invalidate the pending Negotiate token when a redirect crossed to a different origin, effectively leaking an authentication credential to a party it was never intended for (conceptually aligned with credential-exposure classes such as CWE-522 or origin-validation errors like CWE-346; the CVE record itself carries no assigned CWE). Because the token is bearer-like material for the target's Kerberos service, exposure enables potential impersonation of the client against the legitimate Negotiate-protected service, bounded here by the low confidentiality rating in the assessed vector CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N. The affected library code paths are shared by the curl command-line tool and libcurl, but only builds configured and invoked for Negotiate authentication are impacted; the same 8.23.0 batch also fixed a related cross-origin reuse issue for Negotiate connections (CVE-2026-87861) and Negotiate sent to a foreign origin (CVE-2026-94265), indicating a broader credential-scoping review in this release cycle.
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Severity by source
Network-delivered via redirect but needs Negotiate auth plus a cross-origin redirect (AC:H); attacker needs no privileges (PR:N); only confidentiality of credentials is affected (C:L, I/A:N).
Description PRE-NVD
Threat Intelligence Overview
CVE.org
How this decision was reached
The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.
What every action level means
Attack Technique
OS command injection occurs when an application passes unsanitized user input directly into system shell commands.
GitHub PoC
Exploit-DB