Description
NULL pointer dereference in coap_dtls_generate_cookie() in src/coap_openssl.c in OISM libcoap 4.3.5 allows remote attackers to cause a denial of service via a crafted DTLS handshake that triggers SSL_get_SSL_CTX() to return NULL.
Fixed in Linux distributions
Distributions backport fixes, so the version that fixes this vulnerability differs per release — upgrade to at least the version shown. From the distributions' security trackers and advisories.
Debian
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian 14 | libcoap3 | 4.3.5-2 | — |
| Debian 13 | libcoap3 | 4.3.4-1.1+deb13u2 | — |
| Debian 12 | libcoap3 | No fix yet | — |
Ubuntu
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu 26.10 | libcoap3 | No fix yet | — |
| Ubuntu 26.04 LTS | libcoap3 | No fix yet | — |
| Ubuntu 25.10 | libcoap3 | No fix yet | — |
| Ubuntu 24.04 LTS | libcoap3 | No fix yet | — |
| Ubuntu 22.04 LTS | libcoap2 +1 | No fix yet | — |
Show 2 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu 20.04 LTS | libcoap2 | No fix yet | — |
| Ubuntu 18.04 LTS | libcoap | No fix yet | — |
openSUSE
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| openSUSE Tumbleweed | libcoap | 4.3.5a-1.1 | openSUSE-SU-2025:15780-1 |
Advisories 1
- openSUSE-SU-2025:15780-1 libcoap-devel-4.3.5a-1.1 on GA media SUSE / openSUSE Security Updates · Feb 4, 2026