Description
libcurl's TFTP state machine fails to validate state transitions against the
requested transfer direction, accepting opening server responses for both
reads and writes interchangeably. A malicious TFTP server can respond to a
download request in a way that forces the client into transmit mode, prompting
libcurl to consume and transmit data from the handle's persistent
`CURLOPT_READDATA` pointer - including data remaining from unrelated prior
operations, such as an HTTP POST request executed on a reused handle.
Published: 2026-10-20
Score: 8.1 High
EPSS: < 1% Very Low
KEV: No
Impact: Information Disclosure
Action: Patch
AI Analysis

Impact

A flaw was found in curl that allows a malicious TFTP server to confuse the transfer direction. By replying to a download request in a way that forces the client into transmit mode, the server can cause the curl client to send leftover sensitive data from previous operations on a reused connection handle. This unintended data transmission results in information disclosure.

Affected Systems

The vulnerability affects the curl client application whenever it handles TFTP transfers. No specific build or version is listed, so all current releases of curl that support TFTP may be affected.

Risk and Exploitability

The CVSS score is 8.1, indicating a high severity. The EPSS score is < 1%, and the issue is not listed in CISA KEV. The likely attack vector requires an attacker to operate a rogue TFTP server that the client connects to. The exploit relies on a reused TFTP connection handle; if the client reuses a handle that previously transmitted sensitive data, that data can be sent back to the attacker. Consequently, the overall risk is high, and it can expose credentials or other confidential information.

Generated by OpenCVE AI on October 30, 2026 at 14:50 UTC.

Remediation

No solution or workaround provided in the CVE record.

OpenCVE Recommended Actions

  • Update curl to the latest version that addresses the TFTP direction confusion flaw.
  • Avoid reusing curl TFTP connection handles across different servers or clear the handle before reusing it to prevent leakage of prior data.
  • Restrict or disable TFTP usage and, where possible, switch to a secure file‑transfer protocol like SFTP or HTTPS.
  • Monitor network traffic for unexpected uploads originating from curl clients to detect exploitation attempts.

Generated by OpenCVE AI on October 30, 2026 at 14:50 UTC.

Tracking

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Advisories
Source ID Title
Ubuntu USN Ubuntu USN USN-8927-1 curl vulnerabilities
Ubuntu USN Ubuntu USN USN-8932-1 curl vulnerabilities
Ubuntu USN Ubuntu USN USN-8927-2 curl vulnerabilities
History

Fri, 30 Oct 2026 13:30:00 +0000

Type Values Removed Values Added
Metrics cvssV3_1

{'score': 3.7, 'vector': 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N'}

 ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'poc', 'Technical Impact': 'total'}, 'version': '2.0.3'}

cvssV3_1

{'score': 8.1, 'vector': 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H'}

Tue, 20 Oct 2026 20:30:00 +0000

Type Values Removed Values Added
Description A flaw was found in curl. When handling Trivial File Transfer Protocol (TFTP) transfers, a malicious server can trigger information disclosure by responding to a download request in a way that forces the client into transmit mode. Consequently, the client may unintentionally send leftover sensitive data from prior operations on a reused connection handle to the attacker's server. libcurl's TFTP state machine fails to validate state transitions against the requested transfer direction, accepting opening server responses for both reads and writes interchangeably. A malicious TFTP server can respond to a download request in a way that forces the client into transmit mode, prompting libcurl to consume and transmit data from the handle's persistent `CURLOPT_READDATA` pointer - including data remaining from unrelated prior operations, such as an HTTP POST request executed on a reused handle.
Title curl: curl: TFTP direction confusion TFTP direction confusion
References

Sun, 18 Oct 2026 17:00:00 +0000

Type Values Removed Values Added
First Time appeared Curl
Curl curl
Vendors & Products Curl
Curl curl

Sat, 17 Oct 2026 00:30:00 +0000

Type Values Removed Values Added
Description A flaw was found in curl. When handling Trivial File Transfer Protocol (TFTP) transfers, a malicious server can trigger information disclosure by responding to a download request in a way that forces the client into transmit mode. Consequently, the client may unintentionally send leftover sensitive data from prior operations on a reused connection handle to the attacker's server.
Title curl: curl: TFTP direction confusion
Weaknesses CWE-200
References
Metrics threat_severity

None

 cvssV3_1

{'score': 3.7, 'vector': 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N'}

threat_severity

Low

Subscriptions

Curl Curl
cve-icon MITRE

Status: PUBLISHED

Assigner: curl

Published:

Updated: 2026-10-30T12:19:17.432Z

Reserved: 2026-09-16T08:12:48.831Z

Link: CVE-2026-92389

cve-icon Vulnrichment

Updated: 2026-10-30T12:17:34.397Z

cve-icon NVD

Status : Awaiting Analysis

Published: 2026-10-20T21:17:21.457

Modified: 2026-10-30T13:20:53.970

Link: CVE-2026-92389

cve-icon Redhat

Severity : Low

Publid Date: 2026-10-14T12:00:00Z

Links: CVE-2026-92389 - Bugzilla

cve-icon OpenCVE Enrichment

Updated: 2026-10-30T15:00:15Z

Weaknesses
  • CWE-200

    Exposure of Sensitive Information to an Unauthorized Actor