CVE-2026-19931
Negotiate ambient user conn reuse
Description
A flaw in libcurl makes it wrongly reuse an HTTP connection setup for a given hostname using Negotiate authentication, when the initial request is done using empty credentials. This can make user B's request get sent over user A's previously authenticated connection.
INFO
Published Date :
Sept. 6, 2026, 6:17 p.m.
Last Modified :
Sept. 15, 2026, 7:16 a.m.
Remotely Exploit :
Yes !
Source :
2499f714-1537-4658-8207-48ae4bb9eae9
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS | 134c704f-9b21-4f2e-91b3-4a467353bcc0 | |||||
| CVSS 3.1 | CRITICAL | 134c704f-9b21-4f2e-91b3-4a467353bcc0 |
Solution
- Update libcurl to the latest version.
- Reconfigure Negotiate authentication settings.
- Test connection reuse logic carefully.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-19931.
| URL | Resource |
|---|---|
| https://curl.se/docs/CVE-2026-19931.html | Patch Vendor Advisory |
| https://curl.se/docs/CVE-2026-19931.json | Vendor Advisory |
| https://hackerone.com/reports/3923520 | Exploit Mitigation Third Party Advisory |
| https://hackerone.com/reports/3923520 | Exploit Mitigation Third Party Advisory |
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-19931 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-19931
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-19931 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-19931 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
-
CVE Modified by 2499f714-1537-4658-8207-48ae4bb9eae9
Sep. 15, 2026
Action Type Old Value New Value Added CWE CWE-488 Added Affected Affected value modified. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/19xxx/CVE-2026-19931.json">CVE-2026-19931</a> -
Initial Analysis by [email protected]
Sep. 11, 2026
Action Type Old Value New Value Added CPE Configuration OR *cpe:2.3:a:haxx:curl:*:*:*:*:*:*:*:* versions from (including) 7.64.1 up to (excluding) 8.22.0 Added Reference Type curl: https://curl.se/docs/CVE-2026-19931.html Types: Patch, Vendor Advisory Added Reference Type curl: https://curl.se/docs/CVE-2026-19931.json Types: Vendor Advisory Added Reference Type CISA-ADP: https://hackerone.com/reports/3923520 Types: Exploit, Mitigation, Third Party Advisory Added Reference Type curl: https://hackerone.com/reports/3923520 Types: Exploit, Mitigation, Third Party Advisory -
CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0
Sep. 08, 2026
Action Type Old Value New Value Added CVSS V3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H Added CWE CWE-488 Added Reference https://hackerone.com/reports/3923520 Added SSVC {'id': 'CVE-2026-19931', 'role': 'CISA Coordinator', 'options': [{'exploitation': 'poc'}, {'automatable': 'yes'}, {'technicalImpact': 'total'}], 'version': '2.0.3', 'timestamp': '2026-09-08T15:42:15.881334Z'} -
New CVE Received by 2499f714-1537-4658-8207-48ae4bb9eae9
Sep. 06, 2026
Action Type Old Value New Value Added Description A flaw in libcurl makes it wrongly reuse an HTTP connection setup for a given hostname using Negotiate authentication, when the initial request is done using empty credentials. This can make user B's request get sent over user A's previously authenticated connection. Added Affected New affected value received. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/19xxx/CVE-2026-19931.json">CVE-2026-19931</a> Added Reference https://curl.se/docs/CVE-2026-19931.html Added Reference https://curl.se/docs/CVE-2026-19931.json Added Reference https://hackerone.com/reports/3923520