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Fencer Vulns
high 8.1

CVE-2021-22901 in the critical feed json

curl 7.75.0 through 7.76.1 suffers from a use-after-free vulnerability resulting in already freed memory being used when a TLS 1.3 session…

published 2021-06-11 5 y ago modified 2026-10-14 26 d ago also EUVD-2021-10033

cvss
8.1
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
63.5%
EPSS 63.5% chance of exploitation in 30 days, percentile 99.2%
public exploits
0
none known

Summary

curl 7.75.0 through 7.76.1 suffers from a use-after-free vulnerability resulting in already freed memory being used when a TLS 1.3 session ticket arrives over a connection. A malicious server can use this in rare unfortunate circumstances to potentially reach remote code execution in the client. When libcurl at run-time sets up support for TLS 1.3 session tickets on a connection using OpenSSL, it stores pointers to the transfer in-memory object for later retrieval when a session ticket arrives. If the connection is used by multiple transfers (like with a reused HTTP/1.1 connection or multiplexed HTTP/2 connection) that first transfer object might be freed before the new session is established on that connection and then the function will access a memory buffer that might be freed. When using that memory, libcurl might even call a function pointer in the object, making it possible for a remote code execution if the server could somehow manage to get crafted memory content into the correct place in memory.

Patch / fix

  • Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP V3.1.5
  • Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP V3.1.5
  • Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP V3.1.5
  • jbcs-httpd24 jboss core services 1 1-18.jbcs.el7
  • jbcs-httpd24 jboss core services 1 1-18.el8jbcs
  • jbcs-httpd24-apr jboss core services 1 1.6.3-105.jbcs.el7
  • jbcs-httpd24-apr jboss core services 1 1.6.3-105.el8jbcs
  • jbcs-httpd24-curl jboss core services 1 7.77.0-2.jbcs.el7
  • jbcs-httpd24-curl jboss core services 1 7.77.0-2.el8jbcs
  • jbcs-httpd24-httpd jboss core services 1 2.4.37-74.jbcs.el7
  • jbcs-httpd24-httpd jboss core services 1 2.4.37-74.el8jbcs

red hat advisories RHSA-2021:2472

  • curl openSUSE Tumbleweed 7.79.1-1.1

opensuse advisories openSUSE-SU-2024:10582-1

  • curl Alpine 3.24, Alpine 3.23, Alpine 3.22 +10 more 7.77.0-r0

alpine advisories ALPINE-CVE-2021-22901

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • curl CBL-Mariner 2.0 7.76.0-5

azure linux advisories AZL-6360

Azure Linux vulnerability data, Copyright (c) Microsoft Corporation, from https://github.com/microsoft/AzureLinuxVulnerabilityData via OSV, under the MIT licence; changed: normalised to fixed package versions per release. MIT

  • curl Arch Linux 7.77.0-1
  • lib32-curl Arch Linux 7.77.0-1
  • libcurl-compat Arch Linux 7.77.0-1
  • lib32-libcurl-compat Arch Linux 7.77.0-1

arch linux advisories AVG-1995AVG-1996AVG-1997AVG-1998

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2021-22901 updated cvss 8.1

curl: Use-after-free in TLS session handling when using OpenSSL TLS backend

  • Red Hat JBoss Core Services Apache HTTP Server 2.4.37 SP8
    fixed: vendor fix RHSA-2021:2471
  • Red Hat JBoss Core Services on RHEL 7 Server jbcs-httpd24 1-18.jbcs.el7, jbcs-httpd24-runtime 1-18.jbcs.el7, jbcs-httpd24-apr 1.6.3-105.jbcs.el7, jbcs-httpd24-curl 7.77.0-2.jbcs.el7, jbcs-httpd24-httpd 2.4.37-74.jbcs.el7, jbcs-httpd24-jansson 2.11-55.jbcs.el7, +23 more Red Hat JBoss Core Services on RHEL 8 jbcs-httpd24 1-18.el8jbcs, jbcs-httpd24-runtime 1-18.el8jbcs, jbcs-httpd24-apr 1.6.3-105.el8jbcs, jbcs-httpd24-curl 7.77.0-2.el8jbcs, jbcs-httpd24-brotli 1.0.6-40.el8jbcs, jbcs-httpd24-httpd 2.4.37-74.el8jbcs, +30 more
    fixed: vendor fix RHSA-2021:2472
  • Red Hat .NET Core 2.1 on Red Hat Enterprise Linux rh-dotnet21-curl, rh-dotnet21-libcurl Red Hat .NET Core 3.1 on Red Hat Enterprise Linux rh-dotnet31-curl, rh-dotnet31-libcurl Red Hat Ceph Storage 2 curl, libcurl Red Hat Enterprise Linux 6 curl, libcurl Red Hat Enterprise Linux 7 curl, libcurl Red Hat Enterprise Linux 8 curl, libcurl, libcurl-minimal
    +2 more products
    Red Hat Enterprise Linux 9 curl, libcurl, curl-minimal, libcurl-minimal Red Hat Software Collections httpd24-curl, httpd24-libcurl
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

cisa ICSA-23-348-10 updated cvss 8.1

Siemens SIMATIC S7-1500

  • Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AB0) >= 3.1.0, < 3.1.5 Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AC0) >= 3.1.0, < 3.1.5 Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AB0) >= 3.1.0, < 3.1.5 Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AC0) >= 3.1.0, < 3.1.5 Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP (6AG1518-4AX00-4AC0) >= 3.1.0, < 3.1.5
    affected: fixed in V3.1.5, mitigation support.industry.siemens.com

Facts from CISA's republication of the vendor's own advisory (CSAF); the linked advisory is the authoritative source. CISA notification · csaf

cisa ICSA-22-132-13 updated cvss 8.1

Siemens Industrial Devices using libcurl

Facts from CISA's republication of the vendor's own advisory (CSAF); the linked advisory is the authoritative source. CISA notification · csaf

CISA SSVC

Exploitation
none
Automatable
yes
Technical impact
total
Assessed
31 d ago

Exploit prediction

63.53% chance of exploitation in the next 30 days, higher than 99.2% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • curl.se https://curl.se/docs/CVE-2021-22901.html referenced PoC, tagged "exploit" by a source, unverified
  • hackerone.com https://hackerone.com/reports/1180380 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
NVD 3.1 8.1 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
NVD 2.0 6.8 AV:N/AC:M/Au:N/C:P/I:P/A:P

Affected products

  • n/a https://github.com/curl/curl
  • Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP
  • Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP
  • Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP

Classification

Weakness
Technology feeds

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

CPEs and fixed versions use Anchore's correction of NVD's data: Improve version ranges to indicate fix.