The version of openssl installed on the remote host is prior to 1.0.2k-24. It is, therefore, affected by a vulnerability as referenced in the ALAS2-2024-2604 advisory.

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

    Impact summary: A buffer overread can have a range of potential consequencessuch as unexpected application     beahviour or a crash. In particular this issuecould result in up to 255 bytes of arbitrary private data     from memory being sentto the peer leading to a loss of confidentiality. However, only applicationsthat     directly call the SSL_select_next_proto function with a 0 length list ofsupported client protocols are     affected by this issue. This would normally neverbe a valid scenario and is typically not under attacker     control but may occur byaccident in the case of a configuration or programming error in the     callingapplication.

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

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

    In the case of NPN, the protocol permits the client to opportunistically selecta protocol when there is no     overlap. OpenSSL returns the first client protocolin the no overlap case in support of this. The list of     client protocols comesfrom 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 aclient_len of 0 then an     invalid memory pointer will be returned instead. If theapplication uses this output as the opportunistic     protocol then the loss ofconfidentiality will occur.

    This issue has been assessed as Low severity because applications are mostlikely to be vulnerable if they     are using NPN instead of ALPN - but NPN is notwidely used. It also requires an application configuration     or programming error.Finally, this issue would not typically be under attacker control making     activeexploitation 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 ofOpenSSL at this time. The fix will     be included in the next releases when theybecome available. (CVE-2024-5535)

Tenable has extracted the preceding description block directly from the tested product security advisory.

Note that Nessus has not tested for this issue but has instead relied only on the application's self-reported version number.

Detections

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Amazon Linux 2 : openssl (ALAS-2024-2604)

critical Nessus Plugin ID 205731

Version 1.1