CVE-2026-15924

Description

Zephyr's TLS socket layer in subsys/net/lib/sockets/sockets_tls.c keeps a single process-global array, client_cache, of cached client sessions that is shared by every TLS socket context. The functions that mutate and read it — tls_session_save(), tls_session_get(), tls_session_cache_reset(), and the settings restore handler — allocate, free, and dereference each entry's heap buffer (entry->session). Before the fix these accesses were serialized only by the per-socket context mutex ctx->lock (assigned per socket in ctx_set_lock()), which provides no mutual exclusion between different sockets touching the shared cache. Because CONFIG_NET_SOCKETS_TLS_MAX_CLIENT_SESSION_COUNT defaults to 1, any two concurrent client sockets contend for the same slot. A thread in tls_session_get() reading entry->session inside mbedtls_ssl_session_load() can run concurrently with another thread in tls_session_save() that selects the same entry for reuse and executes mbedtls_free(entry->session) before reallocating — a use-after-free read, and a double-free when two saves evict the same entry. Both corrupt the mbedTLS heap. The cache is reached on ordinary client paths: at connect time via tls_session_store()/tls_session_restore(), and (on main) whenever a TLS 1.3 session ticket arrives during recv()/poll() via tls_session_store_current(). Exploitation requires an application that opts into per-socket client session caching (the TLS_SESSION_CACHE socket option, off by default) and runs concurrent TLS client connections on multiple threads; the timing that opens the window is influenced by the remote peer(s), so a malicious or compromised server can raise session-ticket frequency to widen it. The reliably-demonstrable impact is memory corruption leading to a crash or heap corruption (denial of service). The fix adds a dedicated session_cache_lock mutex taken across every accessor of client_cache, serializing all reads and frees and closing the race.

CVSS 3.1

5.9 MEDIUMCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS

0.41% probability · 35th percentile

Public exploits

None in Exploit-DB

CISA KEV

Not listed

Weakness

CWE-416

Source

vulnerabilities@zephyrproject.org

Source: NVD record, EPSS from FIRST.org, KEV from CISA, exploits from Exploit-DB. Refreshed daily. Download this record as JSON.