CVE-2026-4873 Details
Description
A vulnerability exists where a connection requiring TLS incorrectly reuses an existing unencrypted connection from the same connection pool. If an initial transfer is made in clear-text (via IMAP, SMTP, or POP3), a subsequent request to that same host bypasses the TLS requirement and instead transmit data unencrypted.
A vulnerability exists in curl and libcurl versions 7.20.0 through 8.19.0, where connections that require TLS incorrectly reuse unencrypted connections from the same pool. This issue arises when an initial transfer is made in clear text using IMAP, SMTP, or POP3. Subsequent requests to the same host can bypass the TLS requirement, leading to unencrypted data transmission. The vulnerability was introduced when clear-text STARTTLS was added to these protocols in curl 7.20.0.
Users are advised to upgrade to curl and libcurl version 8.20.0, or to apply the patch available in the curl GitHub repository.
Metrics
CVSS 4.0 Severity and Vector Strings:
No CVSS 4.0 data is available for this CVE.
CVSS 3.x Severity and Vector Strings:
No data available for CVSS Version 2.0 on this CVE.
CISA-ADP
Assessed May 13, 2026References to Advisories, Solutions, and Tools
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| URL | Source(s) | Tag(s) |
|---|---|---|
| https://curl.se/docs/CVE-2026-4873.html | curl | PatchVendor Advisory |
| https://curl.se/docs/CVE-2026-4873.json | curl | Vendor Advisory |
| https://hackerone.com/reports/3621851 | curl | ExploitIssue TrackingThird Party Advisory |
| http://www.openwall.com/lists/oss-security/2026/04/29/7 | CVE | Mailing ListPatchThird Party Advisory |
Weakness Enumeration
| CWE-ID | CWE Name | Source |
|---|---|---|
| CWE-295 | Improper Certificate Validation | [email protected] |
| CWE-319 | Cleartext Transmission of Sensitive Information | CISA-ADP |
| CWE-319 | Cleartext Transmission of Sensitive Information | curl |
Affected Products
| Product | Versions |
|---|---|
| haxx curl | >= 7.20.0, < 8.20.0 |
CPE
Remediation
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Change History
8 change records found show changes
| Date | Action | Recorded By |
|---|---|---|
| Sep 15, 2026 | CVE Modified | curl |
| Sep 15, 2026 | CVE Modified | CVE |
| Jun 17, 2026 | CVE Modified | curl |
| Jun 17, 2026 | CVE Modified | CISA-ADP |
| May 14, 2026 | Initial Analysis | [email protected] |
| May 13, 2026 | CVE Modified | CISA-ADP |
| May 13, 2026 | New CVE Received | curl |
| May 13, 2026 | CVE Modified | CVE |