Vulnerability Intelligence

CVE-2021-22947

Medium 5.9

Published
Last modified
NVD status
Modified

Description

When curl >= 7.20.0 and <= 7.78.0 connects to an IMAP or POP3 server to retrieve data using STARTTLS to upgrade to TLS security, the server can respond and send back multiple responses at once that curl caches. curl would then upgrade to TLS but not flush the in-queue of cached responses but instead continue using and trustingthe responses it got *before* the TLS handshake as if they were authenticated.Using this flaw, it allows a Man-In-The-Middle attacker to first inject the fake responses, then pass-through the TLS traffic from the legitimate server and trick curl into sending data back to the user thinking the attacker's injected data comes from the TLS-protected server.

Affected products

haxx: curl; fedoraproject: fedora; debian: debian linux; netapp: cloud backup; netapp: clustered data ontap; netapp: h300s firmware; netapp: h300s; netapp: h500s firmware; netapp: h500s; netapp: h700s firmware; netapp: h700s; netapp: h300e firmware; netapp: h300e; netapp: h500e firmware; netapp: h500e

References10

Metrics

CVSS 3.1
5.9 MEDIUM Score source: NVD CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N
EPSS — exploit probability
3% percentile: 87 · as of 4 November 2026
CWE
CWE-310CWE-345

Could this be exploited in your environment?

A patch closes the known hole. A penetration test shows what an attacker can still reach — with proof.

Request a pentest