CVE-2026-16318

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When a TLS 1.3 connection goes through a HelloRetryRequest, the handler is called twice on the same connection. On the second call, s2n_alloc zeroes the existing pointer before allocating new memory, causing the first allocation to be leaked.\n\n\n\nThis can occur during normal QUIC traffic when a client offers a key share group the server does not prefer. An unauthenticated user can amplify the issue by deliberately forcing HelloRetryRequests, causing up to approximately 64 KB of unreachable memory per handshake. Over time, this can lead to increased memory consumption on long-running server processes. The unreachable memory is only reclaimed when the process is restarted.\n\n\n\nOnly server-side QUIC-enabled deployments are affected. Non-QUIC TLS connections are not affected.\n\n\n\nWe recommend you upgrade s2n-tls to version v1.7.6", "supportingMedia": [{"type": "text/html", "base64": false, "value": "<p>The QUIC transport parameters extension handler in s2n-tls incorrectly uses s2n_alloc instead of s2n_realloc to store the peer's transport parameters. When a TLS 1.3 connection goes through a HelloRetryRequest, the handler is called twice on the same connection. On the second call, s2n_alloc zeroes the existing pointer before allocating new memory, causing the first allocation to be leaked.</p><p>This can occur during normal QUIC traffic when a client offers a key share group the server does not prefer. An unauthenticated user can amplify the issue by deliberately forcing HelloRetryRequests, causing up to approximately 64 KB of unreachable memory per handshake. Over time, this can lead to increased memory consumption on long-running server processes. 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Non-QUIC TLS connections are not affected.</p><p>We recommend you upgrade s2n-tls to version v1.7.6</p>"}]}], "references": [{"url": "https://github.com/aws/s2n-tls/releases/tag/v1.7.6", "tags": ["release-notes", "patch"]}, {"url": "https://staging.prod.website.marketing.aws.dev/security/security-bulletins/2026-062-aws/", "tags": ["vendor-advisory"]}, {"url": "https://github.com/aws/s2n-tls/security/advisories/GHSA-cr7x-863j-xrc7", "tags": ["release-notes"]}], "metrics": [{"format": "CVSS", "scenarios": [{"lang": "en", "value": "GENERAL"}], "cvssV3_1": {"version": "3.1", "attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "NONE", "integrityImpact": "NONE", "availabilityImpact": "LOW", "baseSeverity": "MEDIUM", "baseScore": 5.3, "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L"}}, {"format": "CVSS", "scenarios": [{"lang": "en", "value": "GENERAL"}], "cvssV4_0": {"attackVector": "NETWORK", "attackComplexity": "LOW", "attackRequirements": "NONE", "privilegesRequired": "NONE", "userInteraction": "NONE", "vulnConfidentialityImpact": "NONE", "subConfidentialityImpact": "NONE", "vulnIntegrityImpact": "NONE", "subIntegrityImpact": "NONE", "vulnAvailabilityImpact": "LOW", "subAvailabilityImpact": "NONE", "exploitMaturity": "NOT_DEFINED", "Safety": "NOT_DEFINED", "Automatable": "NOT_DEFINED", "Recovery": "NOT_DEFINED", "valueDensity": "NOT_DEFINED", "vulnerabilityResponseEffort": "NOT_DEFINED", "providerUrgency": "NOT_DEFINED", "version": "4.0", "baseSeverity": "MEDIUM", "baseScore": 6.9, "vectorString": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N"}}], "source": {"discovery": "UNKNOWN"}, "x_generator": {"engine": "Vulnogram 1.0.4"}}, "adp": [{"metrics": [{"other": {"type": "ssvc", "content": {"timestamp": "2026-07-22T19:34:05.501993Z", "id": "CVE-2026-16318", "options": [{"Exploitation": "none"}, {"Automatable": "yes"}, {"Technical Impact": "partial"}], "role": "CISA Coordinator", "version": "2.0.3"}}}], "title": "CISA ADP Vulnrichment", "providerMetadata": {"orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "shortName": "CISA-ADP", "dateUpdated": "2026-07-22T19:41:13.270Z"}}]}}

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When a TLS 1.3 connection goes through a HelloRetryRequest, the handler is called twice on the same connection. On the second call, s2n_alloc zeroes the existing pointer before allocating new memory, causing the first allocation to be leaked.\n\n\n\nThis can occur during normal QUIC traffic when a client offers a key share group the server does not prefer. An unauthenticated user can amplify the issue by deliberately forcing HelloRetryRequests, causing up to approximately 64 KB of unreachable memory per handshake. Over time, this can lead to increased memory consumption on long-running server processes. The unreachable memory is only reclaimed when the process is restarted.\n\n\n\nOnly server-side QUIC-enabled deployments are affected. Non-QUIC TLS connections are not affected.\n\n\n\nWe recommend you upgrade s2n-tls to version v1.7.6", "supportingMedia": [{"type": "text/html", "value": "<p>The QUIC transport parameters extension handler in s2n-tls incorrectly uses s2n_alloc instead of s2n_realloc to store the peer's transport parameters. When a TLS 1.3 connection goes through a HelloRetryRequest, the handler is called twice on the same connection. On the second call, s2n_alloc zeroes the existing pointer before allocating new memory, causing the first allocation to be leaked.</p><p>This can occur during normal QUIC traffic when a client offers a key share group the server does not prefer. An unauthenticated user can amplify the issue by deliberately forcing HelloRetryRequests, causing up to approximately 64 KB of unreachable memory per handshake. Over time, this can lead to increased memory consumption on long-running server processes. 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Over time, this can lead to increased memory consumption on long-running server processes. The unreachable memory is only reclaimed when the process is restarted.\n\n\n\nOnly server-side QUIC-enabled deployments are affected. Non-QUIC TLS connections are not affected.\n\n\n\nWe recommend you upgrade s2n-tls to version v1.7.6"}, {"lang": "es", "value": "El gestor de la extensi\u00f3n de par\u00e1metros de transporte QUIC en s2n-tls utiliza incorrectamente s2n_alloc en lugar de s2n_realloc para almacenar los par\u00e1metros de transporte del par. Cuando una conexi\u00f3n TLS 1.3 pasa por un HelloRetryRequest, el gestor es llamado dos veces en la misma conexi\u00f3n. En la segunda llamada, s2n_alloc pone a cero el puntero existente antes de asignar nueva memoria, lo que provoca una fuga de la primera asignaci\u00f3n.\n\nEsto puede ocurrir durante el tr\u00e1fico QUIC normal cuando un cliente ofrece un grupo de intercambio de claves que el servidor no prefiere. Un usuario no autenticado puede amplificar el problema forzando deliberadamente HelloRetryRequests, causando hasta aproximadamente 64 KB de memoria inalcanzable por handshake. Con el tiempo, esto puede llevar a un aumento del consumo de memoria en procesos de servidor de larga duraci\u00f3n. La memoria inalcanzable solo se recupera cuando el proceso se reinicia.\n\nSolo las implementaciones del lado del servidor con QUIC habilitado se ven afectadas. Las conexiones TLS que no son QUIC no se ven afectadas.\n\nRecomendamos actualizar s2n-tls a la versi\u00f3n v1.7.6"}], "id": "CVE-2026-16318", "lastModified": "2026-10-24T19:10:00.127", "metrics": {"cvssMetricV31": [{"cvssData": {"attackComplexity": "LOW", "attackVector": "NETWORK", "availabilityImpact": "LOW", "baseScore": 5.3, "baseSeverity": "MEDIUM", "confidentialityImpact": "NONE", "integrityImpact": "NONE", "privilegesRequired": "NONE", "scope": "UNCHANGED", "userInteraction": "NONE", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L", "version": "3.1"}, "exploitabilityScore": 3.9, "impactScore": 1.4, "source": "ff89ba41-3aa1-4d27-914a-91399e9639e5", "type": "Secondary"}], "cvssMetricV40": [{"cvssData": {"Automatable": "NOT_DEFINED", "Recovery": "NOT_DEFINED", "Safety": "NOT_DEFINED", "attackComplexity": "LOW", "attackRequirements": "NONE", "attackVector": "NETWORK", "availabilityRequirement": "NOT_DEFINED", "baseScore": 6.9, "baseSeverity": "MEDIUM", "confidentialityRequirement": "NOT_DEFINED", "exploitMaturity": "NOT_DEFINED", "integrityRequirement": "NOT_DEFINED", "modifiedAttackComplexity": "NOT_DEFINED", "modifiedAttackRequirements": "NOT_DEFINED", "modifiedAttackVector": "NOT_DEFINED", "modifiedPrivilegesRequired": "NOT_DEFINED", "modifiedSubAvailabilityImpact": "NOT_DEFINED", "modifiedSubConfidentialityImpact": "NOT_DEFINED", "modifiedSubIntegrityImpact": "NOT_DEFINED", "modifiedUserInteraction": "NOT_DEFINED", "modifiedVulnAvailabilityImpact": "NOT_DEFINED", "modifiedVulnConfidentialityImpact": "NOT_DEFINED", "modifiedVulnIntegrityImpact": "NOT_DEFINED", "privilegesRequired": "NONE", "providerUrgency": "NOT_DEFINED", "subAvailabilityImpact": "NONE", "subConfidentialityImpact": "NONE", "subIntegrityImpact": "NONE", "userInteraction": "NONE", "valueDensity": "NOT_DEFINED", "vectorString": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/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", "version": "4.0", "vulnAvailabilityImpact": "LOW", "vulnConfidentialityImpact": "NONE", "vulnIntegrityImpact": "NONE", "vulnerabilityResponseEffort": "NOT_DEFINED"}, "source": "ff89ba41-3aa1-4d27-914a-91399e9639e5", "type": "Secondary"}], "ssvcV203": [{"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "ssvcData": {"id": "CVE-2026-16318", "options": [{"exploitation": "none"}, {"automatable": "yes"}, {"technicalImpact": "partial"}], "role": "CISA Coordinator", "timestamp": "2026-07-22T19:34:05.501993Z", "version": "2.0.3"}}]}, "published": "2026-07-21T21:16:49.220", "references": [{"source": "ff89ba41-3aa1-4d27-914a-91399e9639e5", "url": "https://github.com/aws/s2n-tls/releases/tag/v1.7.6"}, {"source": "ff89ba41-3aa1-4d27-914a-91399e9639e5", "url": "https://github.com/aws/s2n-tls/security/advisories/GHSA-cr7x-863j-xrc7"}, {"source": "ff89ba41-3aa1-4d27-914a-91399e9639e5", "url": "https://staging.prod.website.marketing.aws.dev/security/security-bulletins/2026-062-aws/"}], "sourceIdentifier": "ff89ba41-3aa1-4d27-914a-91399e9639e5", "vulnStatus": "Awaiting Analysis", "weaknesses": [{"description": [{"lang": "en", "value": "CWE-401"}], "source": "ff89ba41-3aa1-4d27-914a-91399e9639e5", "type": "Secondary"}]}

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