CVE-2021-22947
MEDIUMEPSS 86th pctlDescription
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.
How to fix
TridentStack Control can deploy fixes like this automatically across your Windows, macOS, and Linux fleet. See how it works
Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.
CVSS v3 Vector
Exploitability
Impact
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N
Exploit Intelligence
Elevated risk: more likely to be exploited than 86% of all known CVEs.
References
Related Vulnerabilities
Other CWE-310 (Cryptographic Issues) vulnerabilities, ordered by exploit likelihood. View all
| CVE | Severity | CVSS | EPSS | Exploited | Fix |
|---|---|---|---|---|---|
| CVE-2014-3566 | Low | 3.4 | 100% | - | Fix |
| CVE-2015-4000 | Low | 3.7 | 100% | - | Fix |
| CVE-2015-0204 | Medium | 4.3 | 99% | - | Fix |
| CVE-2016-2107 | Medium | 5.9 | 89% | - | Fix |
| CVE-2016-0800 | Medium | 5.9 | 82% | - | Fix |
| CVE-2014-8684 | Critical | 9.8 | 72% | - | - |
Common questions
How do I fix CVE-2021-22947?
Published advisories record a fix for 18 affected products. The "How to fix" section on this page lists the fixed version and source advisory for each one, so apply the entry matching what you actually run.
Is CVE-2021-22947 being actively exploited?
Not that we know of. CVE-2021-22947 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 3.0% is the estimated probability that it will be exploited in the next 30 days. That is higher than 86% of all scored CVEs.
How severe is CVE-2021-22947?
CVE-2021-22947 has a CVSS v3 base score of 5.9, rated medium. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.
What does CVE-2021-22947 affect?
Published advisories record a fix for curl (Debian), Windows 10 Version 1809 (Windows), Windows 10 Version 1909 (Windows), Windows 10 Version 20H2 (Windows), and 14 more. Only products with a sourced advisory are listed, so treat this as what we can cite rather than a complete inventory.
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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-04-16.