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.
History

Thu, 16 Apr 2026 15:15:00 +0000

Type Values Removed Values Added
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'poc', 'Technical Impact': 'partial'}, 'version': '2.0.3'}


cve-icon MITRE

Status: PUBLISHED

Assigner: hackerone

Published: 2021-09-29T00:00:00.000Z

Updated: 2026-04-16T14:01:05.826Z

Reserved: 2021-01-06T00:00:00.000Z

Link: CVE-2021-22947

cve-icon Vulnrichment

Updated: 2024-08-03T18:58:26.408Z

cve-icon NVD

Status : Modified

Published: 2021-09-29T20:15:08.253

Modified: 2026-04-16T15:16:44.660

Link: CVE-2021-22947

cve-icon Redhat

Severity : Moderate

Publid Date: 2021-09-15T00:00:00Z

Links: CVE-2021-22947 - Bugzilla