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Vulnerability record · CVE-2024-5535 · published 27 June 2024

CVE-2024-5535: Openssl out-of-bounds read vulnerability

OOpenssl · Openssl

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.

9.1 CVSS 3.1 Critical EPSS 6.1% · top 6.5% CWE-125 · Out-of-bounds read
9.1CVSS 3.1 base score
6.1%EPSS exploitation probability, 30 days
NoNot in CISA KEV
36Affected product versions listed by NVD
28References
10 Nov 2026Last modified by NVD

Description

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.

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

Affected products

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

References

LinkTags
https://github.com/openssl/openssl/commit/4ada436a1946cbb24db5ab4ca082b69c1bc10f37 Patch
https://github.com/openssl/openssl/commit/99fb785a5f85315b95288921a321a935ea29a51e Patch
https://github.com/openssl/openssl/commit/cf6f91f6121f4db167405db2f0de410a456f260c Patch
https://github.com/openssl/openssl/commit/e86ac436f0bd54d4517745483e2315650fae7b2c Patch
https://github.openssl.org/openssl/extended-releases/commit/9947251413065a05189a63c9b7a6c1d4e224c21c Permissions Required
https://github.openssl.org/openssl/extended-releases/commit/b78ec0824da857223486660177d3b1f255c65d87 Permissions Required
https://www.openssl.org/news/secadv/20240627.txt Vendor Advisory
http://www.openwall.com/lists/oss-security/2024/06/27/1 Mailing ListThird Party Advisory
http://www.openwall.com/lists/oss-security/2024/06/28/4 Mailing ListThird Party Advisory
http://www.openwall.com/lists/oss-security/2024/08/15/1 Mailing ListThird Party Advisory
https://github.com/openssl/openssl/commit/4ada436a1946cbb24db5ab4ca082b69c1bc10f37 Patch
https://github.com/openssl/openssl/commit/99fb785a5f85315b95288921a321a935ea29a51e Patch
https://github.com/openssl/openssl/commit/cf6f91f6121f4db167405db2f0de410a456f260c Patch
https://github.com/openssl/openssl/commit/e86ac436f0bd54d4517745483e2315650fae7b2c Patch
https://github.openssl.org/openssl/extended-releases/commit/9947251413065a05189a63c9b7a6c1d4e224c21c Permissions Required
https://github.openssl.org/openssl/extended-releases/commit/b78ec0824da857223486660177d3b1f255c65d87 Permissions Required
https://lists.debian.org/debian-lts-announce/2024/10/msg00033.html Mailing ListThird Party Advisory
https://lists.debian.org/debian-lts-announce/2024/11/msg00000.html Mailing ListThird Party Advisory
https://security.netapp.com/advisory/ntap-20240712-0005/ Third Party Advisory
https://security.netapp.com/advisory/ntap-20241025-0006/ Third Party Advisory
https://security.netapp.com/advisory/ntap-20241025-0010/ Third Party Advisory
https://www.openssl.org/news/secadv/20240627.txt Vendor Advisory
https://cert-portal.siemens.com/productcert/html/ssa-265688.html Third Party Advisory
https://cert-portal.siemens.com/productcert/html/ssa-277137.html Third Party Advisory
https://cert-portal.siemens.com/productcert/html/ssa-398330.html Third Party Advisory
https://cert-portal.siemens.com/productcert/html/ssa-613116.html Third Party Advisory
https://cert-portal.siemens.com/productcert/html/ssa-769027.html Third Party Advisory
https://cert-portal.siemens.com/productcert/html/ssa-915275.html Third Party Advisory

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Source: NIST National Vulnerability Database (record CVE-2024-5535), CISA KEV, FIRST EPSS (scores of 2026-11-12). This page is refreshed as NVD updates the record.