FreeBSD: VID-21F505F4-6A1C-11EF-B611-84A93843EB75 (CVE-2024-5535): OpenSSL -- Multiple vulnerabilities

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.