SSL_select_next_proto buffer overread

published 2024-06-27 2 y ago modified 2026-11-06 2 d ago also EUVD-2024-46737 , GHSA-4fc7-mvrr-wv2c , JLSEC-2026-252

cvss: 9.1; version 3.1, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 5.6%; EPSS 5.6% chance of exploitation in 30 days, percentile 92%
public exploits: 0; none known

Issue summary: Calling the OpenSSL API function SSL_select_next_proto with an empty supported client protocols buffer may cause a crash or memory contents to be sent to the peer.

Impact summary: A buffer overread can have a range of potential consequences such as unexpected application beahviour or a crash. In particular this issue could result in up to 255 bytes of arbitrary private data from memory being sent to the peer leading to a loss of confidentiality. However, only applications that directly call the SSL_select_next_proto function with a 0 length list of supported client protocols are affected by this issue. This would normally never be a valid scenario and is typically not under attacker control but may occur by accident in the case of a configuration or programming error in the calling application.

The OpenSSL API function SSL_select_next_proto is typically used by TLS applications that support ALPN (Application Layer Protocol Negotiation) or NPN (Next Protocol Negotiation). NPN is older, was never standardised and is deprecated in favour of ALPN. We believe that ALPN is significantly more widely deployed than NPN. The SSL_select_next_proto function accepts a list of protocols from the server and a list of protocols from the client and returns the first protocol that appears in the server list that also appears in the client list. In the case of no overlap between the two lists it returns the first item in the client list. In either case it will signal whether an overlap between the two lists was found. In the case where SSL_select_next_proto is called with a zero length client list it fails to notice this condition and returns the memory immediately following the client list pointer (and reports that there was no overlap in the lists).

This function is typically called from a server side application callback for ALPN or a client side application callback for NPN. In the case of ALPN the list of protocols supplied by the client is guaranteed by libssl to never be zero in length. The list of server protocols comes from the application and should never normally be expected to be of zero length. In this case if the SSL_select_next_proto function has been called as expected (with the list supplied by the client passed in the client/client_len parameters), then the application will not be vulnerable to this issue. If the application has accidentally been configured with a zero length server list, and has accidentally passed that zero length server list in the client/client_len parameters, and has additionally failed to correctly handle a "no overlap" response (which would normally result in a handshake failure in ALPN) then it will be vulnerable to this problem.

In the case of NPN, the protocol permits the client to opportunistically select a protocol when there is no overlap. OpenSSL returns the first client protocol in the no overlap case in support of this. The list of client protocols comes from the application and should never normally be expected to be of zero length. However if the SSL_select_next_proto function is accidentally called with a client_len of 0 then an invalid memory pointer will be returned instead. If the application uses this output as the opportunistic protocol then the loss of confidentiality will occur.

This issue has been assessed as Low severity because applications are most likely to be vulnerable if they are using NPN instead of ALPN - but NPN is not widely used. It also requires an application configuration or programming error. Finally, this issue would not typically be under attacker control making active exploitation unlikely.

The FIPS modules in 3.3, 3.2, 3.1 and 3.0 are not affected by this issue.

Due to the low severity of this issue we are not issuing new releases of OpenSSL at this time. The fix will be included in the next releases when they become available.

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-2024-5535 updated 2026-11-07 cvss 5.9

openssl: SSL_select_next_proto buffer overread

Red Hat Logging Subsystem for Red Hat OpenShift openshift-logging/fluentd-rhel8 Red Hat 3scale API Management Platform 2 3scale-amp2/backend-rhel8
affected: workaround, no fix available “Fix deferred”
Red Hat Enterprise Linux 7 ovmf, OVMF, AAVMF Red Hat Enterprise Linux 8 edk2, edk2-ovmf, edk2-aarch64, compat-openssl10
affected: workaround, no fix available
Red Hat Enterprise Linux 9 edk2, edk2-ovmf, edk2-tools, edk2-aarch64, compat-openssl11 Red Hat JBoss Web Server 5 openssl
affected: workaround, no fix available “Fix deferred”
Red Hat OpenShift Container Platform 4 openshift/ose-rhel-coreos-9
affected: workaround, no fix available
Red Hat Software Collections rh-mysql80-mysql, rh-mysql80-mysql-test, rh-mysql80-mysql-common, rh-mysql80-mysql-config, rh-mysql80-mysql-errmsg, rh-mysql80-mysql-server, +4 more
affected: workaround, no fix planned “Out of support scope”
Red Hat Trusted Profile Analyzer trustification-product-1-0-z
affected: workaround, no fix available
Red Hat CodeReady Linux Builder (v. 9) mysql-libs 8.0.41-2.el9_5, mysql-test 8.0.41-2.el9_5
fixed: vendor fix RHSA-2025:1671
Red Hat Enterprise Linux AppStream (v. 8) mecab 0.996-2.module+el8.10.0+22857+7f331edd, mysql 8.0.41-1.module+el8.10.0+22857+7f331edd, mysql-libs 8.0.41-1.module+el8.10.0+22857+7f331edd, mysql-test 8.0.41-1.module+el8.10.0+22857+7f331edd, mysql-common 8.0.41-1.module+el8.10.0+22857+7f331edd, mysql-errmsg 8.0.41-1.module+el8.10.0+22857+7f331edd, +3 more
fixed: vendor fix RHSA-2025:1673

show 17 more

Red Hat Enterprise Linux AppStream (v. 9) mysql 8.0.41-2.el9_5, openssl-perl 3.2.2-6.el9_5, mysql-common 8.0.41-2.el9_5, mysql-errmsg 8.0.41-2.el9_5, mysql-server 8.0.41-2.el9_5
fixed: vendor fix RHSA-2024:9333
Red Hat Enterprise Linux AppStream EUS (v.9.4) openssl-perl 3.0.7-29.el9_4
fixed: vendor fix RHSA-2025:3666
Red Hat Enterprise Linux BaseOS (v. 8) openssl 1.1.1k-14.el8_6, openssl-libs 1.1.1k-14.el8_6, openssl-perl 1.1.1k-14.el8_6
fixed: vendor fix RHSA-2024:7848
Red Hat Enterprise Linux BaseOS (v. 9) openssl 3.2.2-6.el9_5, openssl-libs 3.2.2-6.el9_5
fixed: vendor fix RHSA-2024:9333
Red Hat Enterprise Linux BaseOS AUS (v.8.6) openssl 1.1.1k-14.el8_6, openssl-libs 1.1.1k-14.el8_6, openssl-perl 1.1.1k-14.el8_6 Red Hat Enterprise Linux BaseOS E4S (v.8.6) openssl 1.1.1k-14.el8_6, openssl-libs 1.1.1k-14.el8_6, openssl-perl 1.1.1k-14.el8_6
fixed: vendor fix RHSA-2024:7846
Red Hat Enterprise Linux BaseOS EUS (v.8.8) openssl 1.1.1k-14.el8_6, openssl-libs 1.1.1k-14.el8_6, openssl-perl 1.1.1k-14.el8_6
fixed: vendor fix RHSA-2024:7847
Red Hat Enterprise Linux BaseOS EUS (v.9.4) openssl 3.0.7-29.el9_4, openssl-libs 3.0.7-29.el9_4
fixed: vendor fix RHSA-2025:3666
Red Hat Enterprise Linux BaseOS TUS (v.8.6) openssl 1.1.1k-14.el8_6, openssl-libs 1.1.1k-14.el8_6, openssl-perl 1.1.1k-14.el8_6
fixed: vendor fix RHSA-2024:7846
Red Hat Enterprise Linux CRB (v. 8) mingw-openssl 1.0.2k-4.el8_10, mingw32-openssl 1.0.2k-4.el8_10, mingw64-openssl 1.0.2k-4.el8_10
fixed: vendor fix RHSA-2026:60329
Red Hat Enterprise Linux Server -EXTENSION(v. 6 ELS-EXTENSION) openssl 1.0.1e-61.el6_10.1
fixed: vendor fix RHSA-2026:66524
Red Hat Enterprise Linux Server (v. 7 ELS) openssl 1.0.2k-26.el7_9.2, openssl-libs 1.0.2k-26.el7_9.2
fixed: vendor fix RHSA-2026:58563
Red Hat Enterprise Linux Server Optional -EXTENSION (v. 6 ELS -EXTENSION) openssl-static 1.0.1e-61.el6_10.1
fixed: vendor fix RHSA-2026:66524
Red Hat Enterprise Linux Server Optional (v. 7 ELS) openssl-perl 1.0.2k-26.el7_9.2
fixed: vendor fix RHSA-2026:58563
Red Hat JBoss Core Services 2.4.62
fixed: vendor fix RHSA-2025:3453
Red Hat JBoss Core Services on RHEL 7 Server jbcs-httpd24-openssl 1.1.1k-19.el7jbcs, jbcs-httpd24-openssl-libs 1.1.1k-19.el7jbcs, jbcs-httpd24-openssl-perl 1.1.1k-19.el7jbcs
fixed: vendor fix RHSA-2025:3452
Red Hat OpenShift AI 8 rhoai/odh-rhel8-operator v2.13.1-2, rhoai/odh-dashboard-rhel8 v2.13.1-1, rhoai/odh-modelmesh-rhel8 v2.13.1-1, rhoai/odh-operator-bundle v2.13.1-2, rhoai/odh-rhel8-operator v2.14.0-24, rhoai/odh-dashboard-rhel8 v2.14.0-11, +56 more
fixed: vendor fix RHBA-2024:8413
Red Hat Enterprise Linux 6 mysql, mysql-libs, mysql-test, mysql-bench, mysql-server, mysql-embedded Red Hat Enterprise Linux 8 shim, shim-x64, shim-aa64, shim-ia32, shim-unsigned-x64 Red Hat Enterprise Linux 9 shim, shim-x64, shim-aa64, shim-unsigned-x64, shim-unsigned-aarch64 Red Hat Enterprise Linux 10 edk2, shim, openssl, mysql8.4 Red Hat Enterprise Linux BaseOS (v. 9) openssl-fips-provider 3.0.7-6.el9_5, openssl-fips-provider-so 3.0.7-6.el9_5 Red Hat Enterprise Linux Server -EXTENSION(v. 6 ELS-EXTENSION) openssl-devel 1.0.1e-61.el6_10.1, openssl-debuginfo 1.0.1e-61.el6_10.1

+6 more productsfewer

Red Hat Enterprise Linux Server (v. 7 ELS) openssl-debuginfo 1.0.2k-26.el7_9.2 Red Hat Enterprise Linux Server Optional -EXTENSION (v. 6 ELS -EXTENSION) openssl-perl 1.0.1e-61.el6_10.1 Red Hat Enterprise Linux Server Optional (v. 7 ELS) openssl-debuginfo 1.0.2k-26.el7_9.2 Red Hat JBoss Core Services on RHEL 7 Server jbcs-httpd24-apr 1.7.5-3.el7jbcs, jbcs-httpd24-curl 8.11.0-2.el7jbcs, jbcs-httpd24-brotli 1.1.0-5.el7jbcs, jbcs-httpd24-httpd 2.4.62-5.el7jbcs, jbcs-httpd24-jansson 2.14-4.el7jbcs, jbcs-httpd24-mod_md 2.4.28-9.el7jbcs, +24 more Red Hat JBoss Core Services on RHEL 8 jbcs-httpd24-apr 1.7.5-3.el8jbcs, jbcs-httpd24-httpd 2.4.62-5.el8jbcs, jbcs-httpd24-mod_md 2.4.28-9.el8jbcs, jbcs-httpd24-apr-util 1.6.3-2.el8jbcs, jbcs-httpd24-mod_ssl 2.4.62-5.el8jbcs, jbcs-httpd24-mod_ldap 2.4.62-5.el8jbcs, +17 more Red Hat Satellite 6 python-pyOpenSSL, python3-pyOpenSSL, python3.12-pyOpenSSL

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-24-102-01 updated 2026-05-14 cvss 5.9

Siemens SIMATIC S7-1500 TM MFP

Siemens SIMATIC S7-1500 TM MFP - GNU/Linux subsystem
affected: mitigation, no fix available