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Vulnerability record · CVE-2021-22947 · published 29 September 2021

CVE-2021-22947: Haxx curl insufficient verification of data authenticity vulnerability

Haxx · Curl

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.

5.9 CVSS 3.1 Medium EPSS 3.0% · top 13.1% CWE-310 · CWE-310CWE-345 · Insufficient verification of data authenticity
5.9CVSS 3.1 base score, v2 4.3
3.0%EPSS exploitation probability, 30 days
NoNot in CISA KEV
26Affected product versions listed by NVD
30References, 2 tagged exploit
17 Jun 2026Last modified by NVD

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.

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

Affected products

26 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
http://seclists.org/fulldisclosure/2022/Mar/29 Mailing ListThird Party Advisory
https://cert-portal.siemens.com/productcert/pdf/ssa-389290.pdf PatchThird Party Advisory
https://hackerone.com/reports/1334763 ExploitIssue TrackingThird Party Advisory
https://lists.debian.org/debian-lts-announce/2021/09/msg00022.html Mailing ListThird Party Advisory
https://lists.debian.org/debian-lts-announce/2022/08/msg00017.html Mailing ListThird Party Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/APOAK4X73EJTAPTSVT7IRVD Mailing ListThird Party Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/RWLEC6YVEM2HWUBX67SDGPS Mailing ListThird Party Advisory
https://security.gentoo.org/glsa/202212-01 Third Party Advisory
https://security.netapp.com/advisory/ntap-20211029-0003/ Third Party Advisory
https://support.apple.com/kb/HT213183 Release NotesThird Party Advisory
https://www.debian.org/security/2022/dsa-5197 Third Party Advisory
https://www.oracle.com/security-alerts/cpuapr2022.html PatchThird Party Advisory
https://www.oracle.com/security-alerts/cpujan2022.html PatchThird Party Advisory
https://www.oracle.com/security-alerts/cpujul2022.html PatchThird Party Advisory
https://www.oracle.com/security-alerts/cpuoct2021.html PatchThird Party Advisory
http://seclists.org/fulldisclosure/2022/Mar/29 Mailing ListThird Party Advisory
https://cert-portal.siemens.com/productcert/pdf/ssa-389290.pdf PatchThird Party Advisory
https://hackerone.com/reports/1334763 ExploitIssue TrackingThird Party Advisory
https://lists.debian.org/debian-lts-announce/2021/09/msg00022.html Mailing ListThird Party Advisory
https://lists.debian.org/debian-lts-announce/2022/08/msg00017.html Mailing ListThird Party Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/APOAK4X73EJTAPTSVT7IRVD Mailing ListThird Party Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/RWLEC6YVEM2HWUBX67SDGPS Mailing ListThird Party Advisory
https://security.gentoo.org/glsa/202212-01 Third Party Advisory
https://security.netapp.com/advisory/ntap-20211029-0003/ Third Party Advisory
https://support.apple.com/kb/HT213183 Release NotesThird Party Advisory
https://www.debian.org/security/2022/dsa-5197 Third Party Advisory
https://www.oracle.com/security-alerts/cpuapr2022.html PatchThird Party Advisory
https://www.oracle.com/security-alerts/cpujan2022.html PatchThird Party Advisory
https://www.oracle.com/security-alerts/cpujul2022.html PatchThird Party Advisory
https://www.oracle.com/security-alerts/cpuoct2021.html PatchThird Party Advisory

Track CVE-2021-22947 inside VULONE

Watch it alongside the ransomware crews, C2 infrastructure and forum chatter that reference it, query it through the API and pull it into your SIEM over TAXII.

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Same products first, then exploited flaws of the same weakness class.

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Source: NIST National Vulnerability Database (record CVE-2021-22947), CISA KEV, FIRST EPSS (scores of 2026-09-28). This page is refreshed as NVD updates the record.