CVE-2021-22947
curl: Server responses received before STARTTLS processed after TLS handshake
Severity
ModerateRed Hat Product Security
CVSS 3.1
Review impact separately from score.
Published · September 15, 2021
Updated · June 28, 2026
Description
A flaw was found in curl. The flaw lies in how curl handles cached or pipelined responses that it receives from either a IMAP, POP3, SMTP or FTP server before the TLS upgrade using STARTTLS. In such a scenario curl even after upgrading to TLS would trust these cached responses treating them as valid and authenticated and use them. An attacker could potentially use this flaw to carry out a Man-In-The-Middle attack. The highest threat from this vulnerability is to data confidentiality.
CVSS score applicability
The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.
Mitigation
No mitigation is specified in collected source.
CVSS / CWE
CVSS 3.1 · 6.1CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:H/I:N/A:N
CWE-319 · Cleartext Transmission of Sensitive Information