Medium severity · published May 13, 2026
CVE-2026-4873
connection reuse ignores TLS requirement
5.9
CVSS
0.3%
EPSS
No
On KEV
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.
CVSS vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
Attack vector
Network
Complexity
High
Privileges
None
User interaction
None
Confidentiality
High
Integrity
None
Availability
None
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.3% · higher than 26% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
CU
curl · curl
7.20.0 before 8.14.2; 8.15.0 before 8.16.1; 8.17.0 before 8.20.0; ec3bb8f727405642a471b4b1b9eb0118fc003104 before 507e7be573b0a76fca597b75ff7cb27a66e7d865; 8.19.0; 8.18.0; +34 more · source: vendor, NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-4873
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-4873
Patch
https://curl.se/docs/CVE-2026-4873.html
Vendor Advisory
https://curl.se/docs/CVE-2026-4873.json
Exploit
https://hackerone.com/reports/3621851
Mailing List
http://www.openwall.com/lists/oss-security/2026/04/29/7
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