CVE-2026-4873

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 v3.1 Score

5.9

MEDIUM

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N

EPSS — Exploit Prediction

0.0001

Probability of exploitation

0.03%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-295 CWE-295

CWE-319 CWE-319

Affected Products

Vendor	Product	Versions
haxx	curl	7.20.0 — 8.20.0

References

Advisories & Patches

https://curl.se/docs/CVE-2026-4873.html https://curl.se/docs/CVE-2026-4873.json http://www.openwall.com/lists/oss-security/2026/04/29/7

Exploits

https://hackerone.com/reports/3621851

Frequently Asked Questions

What is CVE-2026-4873? +

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. It has a CVSS v3.1 base score of 5.9 (MEDIUM).

How severe is CVE-2026-4873? +

CVE-2026-4873 has a CVSS v3.1 score of 5.9 out of 10, rated MEDIUM. This is a medium-severity vulnerability that should be remediated as part of regular maintenance. The EPSS score is 0.0001, placing it in the 0th percentile for exploitation probability.

What products are affected by CVE-2026-4873? +

CVE-2026-4873 affects products from haxx, specifically: curl. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2026-4873? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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