EUVD-2026-56820Severity by source
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Network-reachable unauthenticated attack with no complexity barrier beyond port rotation; impact is availability-only with no confidentiality or integrity effect.
Primary rating from Vendor (github).
CVSS VectorVendor: github
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Lifecycle Timeline
4DescriptionCVE.org
Coturn is a free open source implementation of TURN and STUN Server. Prior to 4.16.0, dtls_server_input_handler() and create_new_connected_udp_socket() in src/apps/relay/dtls_listener.c retain OpenSSL dtls1_reassemble_fragment() state for a 35-byte fragmented ClientHello declaring a 650,000-byte handshake before cookie validation, allowing an unauthenticated remote sender using fresh UDP tuples to exhaust memory without TURN credentials, a completed handshake, a valid cookie, or source spoofing. This issue is fixed in version 4.16.0.
AnalysisAI
Memory exhaustion in Coturn's DTLS listener allows unauthenticated remote attackers to crash or degrade the TURN/STUN service by flooding it with fragmented DTLS ClientHello messages before cookie validation occurs. All Coturn deployments prior to version 4.16.0 are affected, as both dtls_server_input_handler() and create_new_connected_udp_socket() in dtls_listener.c retain OpenSSL reassembly state for attacker-declared inflated handshake lengths without first completing RFC 6347 cookie exchange. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | The attacker must have UDP connectivity to the Coturn DTLS listener port (commonly UDP 3478 or 5349). … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | The CVSS 4.0 score of 8.2 with vector AV:N/AC:L/AT:P/PR:N/UI:N reflects a network-reachable, unauthenticated attack with no user interaction required, with AT:P (Attack Requirements: Present) indicating the attacker must supply fresh UDP source tuples per ClientHello to bypass per-source limiting - a low but nonzero bar. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | An attacker with UDP connectivity to the Coturn DTLS listener sends a continuous stream of 35-byte fragmented DTLS ClientHello messages, each declaring a 650,000-byte total handshake length and each originating from a distinct UDP source tuple via port rotation. For each message, Coturn allocates a per-peer SSL context and OpenSSL fragment reassembly buffer based on the declared length before any cookie validation, accumulating hundreds of megabytes of heap memory until the process is terminated by the OS OOM killer or becomes unresponsive. … |
| Remediation | Upgrade Coturn to version 4.16.0 or later, available at https://github.com/coturn/coturn/releases/tag/4.16.0. … Detailed patch versions, workarounds, and compensating controls in full report. |
Recommended ActionAI
Within 24 hours, inventory all Coturn deployments and their current versions across production and staging environments. …
Sign in for detailed remediation steps and compensating controls.
Threat intelligence, references, and detailed analysis are available after sign-in.
The (1) TLS and (2) DTLS implementations in OpenSSL 1.0.1 before 1.0.1g do not properly handle Heartbeat Extension packe
The dtls1_reassemble_fragment function in d1_both.c in OpenSSL before 0.9.8za, 1.0.0 before 1.0.0m, and 1.0.1 before 1.0
OpenSSL before 0.9.8za, 1.0.0 before 1.0.0m, and 1.0.1 before 1.0.1h does not properly restrict processing of ChangeCiph
The SSLv2 protocol, as used in OpenSSL before 1.0.1s and 1.0.2 before 1.0.2g and other products, requires a server to se
The ssl3_get_key_exchange function in s3_clnt.c in OpenSSL before 0.9.8zd, 1.0.0 before 1.0.0p, and 1.0.1 before 1.0.1k
The SSL protocol 3.0, as used in OpenSSL through 1.0.1i and other products, uses nondeterministic CBC padding, which mak
The AES-NI implementation in OpenSSL before 1.0.1t and 1.0.2 before 1.0.2h does not consider memory allocation during a
The X509_verify_cert function in crypto/x509/x509_vfy.c in OpenSSL 1.0.1n, 1.0.1o, 1.0.2b, and 1.0.2c does not properly
A buffer overrun can be triggered in X.509 certificate verification, specifically in name constraint checking. Rated hig
The ssl3_send_client_key_exchange function in s3_clnt.c in OpenSSL before 0.9.8za, 1.0.0 before 1.0.0m, and 1.0.1 before
In OpenSSL 1.1.0 before 1.1.0d, if a malicious server supplies bad parameters for a DHE or ECDHE key exchange then this
A denial of service flaw was found in OpenSSL 0.9.8, 1.0.1, 1.0.2 through 1.0.2h, and 1.1.0 in the way the TLS/SSL proto
Same weakness CWE-400 – Uncontrolled Resource Consumption
View allSame technique Denial Of Service
View allVendor StatusVendor
SUSE
Severity: ModerateShare
External POC / Exploit Code
Leaving vuln.today