OpenSSL: raw-public-key endpoints with no certificate abort on a peer-sent signature_algorithms_cert extension

Impact

When an OpenSSL server or client is configured for RFC 7250 raw public keys and has only a private key loaded with no matching certificate, a peer that solicits raw public keys and also sends the normally-omitted signature_algorithms_cert extension triggers a NULL pointer dereference. OpenSSL scopes the impact to denial of service via application abort - no data disclosure, no code execution. The configuration is uncommon: OpenSSL's own guidance is to always pair the private key with a certificate, and doing so makes the extension handling reliable even on unpatched builds. Relevant to a fleet mainly where RPK was chosen deliberately for machine-to-machine links between control-plane components, since the abort takes down the whole process.

Who can reach it

Any peer that can open a TLS connection to the affected endpoint, or any server an affected client connects to. No authentication required. Only key-only RPK configurations are exposed.

What to do

Two options. The cheap one, available now, is to configure a matching certificate alongside the private key - self-signed or signed by any convenient CA - which the advisory states makes signature_algorithms_cert handling reliable without the code fix, and which also lets non-RPK peers connect. The durable one is to upgrade to the fixed OpenSSL release named in the 2026-08-25 advisory and restart every service linked against libssl. The record does not give a fixed version for this CVE; read it off the advisory.

References

Related entries

• OpenSSL QUIC: malformed INITIAL packet double-frees the record-layer object and kills the server processCVE-2026-18798 · OpenSSL QUIC server (port_default_packet_handler / port_bind_channel QRX object)High
• Linux kernel (drivers/nvme/target): Ordinary client I/O to an nvmet block-device namespace can hit a completion raceCVE-2026-23148 · Linux kernel (drivers/nvme/target)High
• Linux kernel (net/tls): The queue that pins encrypted input buffers while the AEAD engine still references them wasCVE-2026-23414 · Linux kernel (net/tls)High
• Linux kernel mlx5_core IPsec full offload (ESN handling): The extended-sequence-number wrap event can be processedCVE-2026-23440 · Linux kernel mlx5_core IPsec full offload (ESN handling)High
• Linux kernel (net/xfrm): One crafted inner IPv4 header (tot_len = 0) inside an IPTFS payload puts the receive path intoCVE-2026-31472 · Linux kernel (net/xfrm)High
• Linux kernel (net/xfrm): A peer that mixes zero-copy-eligible and copy-path IPTFS fragments in one datagram makesCVE-2026-31517 · Linux kernel (net/xfrm)High