CVE-2021-22947

5.9 MEDIUM 3% exploit odds Fix listed

What it is

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.

At a glance

Exploitability: Can be exploited over the network without logging in. High risk of data tampering.
Exploit odds: 3.0% chance of exploitation in the next 30 days (EPSS).
Fix: A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

2021-09-29 20:15 UTC PublishedDisclosed publicly on CVE.org and NVD
2026-10-14 12:17 UTC Last updatedMost recent change to the record

Why it ranks here

Exploited in the wild: no, CISA does not list it.
Exploit odds: 3.0% in the next 30 days (EPSS).
Severity: 5.9 MEDIUM (CVSS).
Fix: a patch or advisory is linked.

Details

Published: 2021-09-29 20:15 UTC
Last modified: 2026-10-14 12:17 UTC
Exploit probability: 3.0% · EPSS, next 30 days
Weakness: CWE-310
Record status: Modified

Affected

Haxx Curl < 7.79.0
Fedoraproject Fedora 33
Fedoraproject Fedora 35
Debian Linux 9.0
Debian Linux 10.0
Debian Linux 11.0
Netapp Cloud Backup
Netapp Clustered Data Ontap

Attack profile CVSS 3.1 · 5.9

Attack vector: Network
Complexity: High
Privileges needed: None
User interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: High
Availability: None

Raw vector

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

Is it in your code?

Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.

Read https://cve-list.com/agent/cve/CVE-2021-22947.md and follow it. Check whether this project is affected by CVE-2021-22947. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.

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Fix and advisories

References

NVD record · CVE.org record