OpenSSL: Out-of-bounds Read

What to do

1. Update OpenSSL to 3.3.2 or 3.2.3 or 3.1.7 or 3.0.15, whichever matches your release line, or a later version.
2. Update RUGGEDCOM RST2428P to V3.1 or a later version.
3. Update SCALANCE XCM-/XRM-/XCH-/XRH-300 family to V3.1 or a later version.
4. Read the advisory on openssl.org for workarounds and exact fixed builds.
5. Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.

Affected products and versions

Version data comes from the organisation that assigned the CVE; 18 further products are omitted here. Confirm against the vendor advisory before deciding you are unaffected.

How the severity score breaks down

Attack vector

NetworkCan be exploited remotely over a network, including the internet.

Attack complexity

LowNo special conditions are needed; the attack works reliably.

Privileges required

NoneNo account or login is needed.

User interaction

NoneNo action by a victim is required.

Scope

UnchangedImpact stays within the vulnerable component.

Confidentiality

HighAll data handled by the component can be read.

Integrity

NoneNothing can be modified.

Availability

HighThe component can be taken down completely.

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H. Scored by CISA (ADP).

Official 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.

Source: the CVE record as published by its numbering authority, via NVD and CVE.org.

The underlying weakness: Out-of-bounds Read

Timeline

1. June 27, 2024CVE record published.
2. November 8, 2024CISA published its SSVC assessment (exploitation: none, automatable: yes, technical impact: partial).
3. November 10, 2026Record last changed materially (score, affected products, status or references).

References

Other vulnerabilities in OpenSSL

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• 7.5 High severity

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• 8.2 High severity

  OpenSSL: Out-of-bounds Read

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  OpenSSL: Out-of-bounds Write

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• 7.5 High severity

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  CVE-2026-54873Sep 29, 2026OpenSSL
• 9.1 Critical severity

  OpenSSL: Improper Validation of Integrity Check Value

  CVE-2026-75803Aug 25, 2026OpenSSL

Recent Out-of-bounds Read vulnerabilities

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