{“lastseen”:”2025-10-08T07:25:45″,”description”:”## Summary:\\nIn curl\u2019s OpenSSL backend, `ossl_get_channel_binding` retains a new reference to the server\u2019s X509 certificate via `SSL_get1_peer_certificate` and never releases it. When Negotiate (SPNEGO) over TLS is in use, this path is invoked and leaks one X509 object per trigger. Over many requests in a long\u2011running libcurl client, this leads to unbounded memory growth and potential denial\u2011of\u2011service.\\n\\nThis occurs only with the OpenSSL backend (\\u003e= 1.1.0 gate present), when curl\/libcurl is built with GSSAPI (`HAVE_GSSAPI`), over HTTPS when a Negotiate challenge is processed.\\n\\nNotes:\\n- The Negotiate challenge over HTTPS is sufficient to trigger channel binding retrieval; a functional Kerberos setup is not required for this leak to manifest.\\n- Each trigger leaks one X509 reference.\\n\\n## Supporting Material\/References:\\n- Code location showing missing X509_free on all paths:\\n“`5650:5679:curl\/lib\/vtls\/openssl.c\\n cert = SSL_get1_peer_certificate(octx-\\u003essl);\\n if(!cert) {\\n \/* No server certificate, don’t do channel binding *\/\\n return CURLE_OK;\\n }\\n\\n if(!OBJ_find_sigid_algs(X509_get_signature_nid(cert), \\u0026algo_nid, NULL)) {\\n failf(data,\\n \\”Unable to find digest NID for certificate signature algorithm\\”);\\n return CURLE_SSL_INVALIDCERTSTATUS;\\n }\\n\\n \/* https:\/\/datatracker.ietf.org\/doc\/html\/rfc5929#section-4.1 *\/\\n if(algo_nid == NID_md5 || algo_nid == NID_sha1) {\\n algo_type = EVP_sha256();\\n }\\n else {\\n algo_type = EVP_get_digestbynid(algo_nid);\\n if(!algo_type) {\\n algo_name = OBJ_nid2sn(algo_nid);\\n failf(data, \\”Could not find digest algorithm %s (NID %d)\\”,\\n algo_name ? algo_name : \\”(null)\\”, algo_nid);\\n return CURLE_SSL_INVALIDCERTSTATUS;\\n }\\n }\\n\\n if(!X509_digest(cert, algo_type, buf, \\u0026length)) {\\n failf(data, \\”X509_digest() failed\\”);\\n return CURLE_SSL_INVALIDCERTSTATUS;\\n }\\n“`\\n\\n“`5681:5688:curl\/lib\/vtls\/openssl.c\\n \/* Append \\”tls-server-end-point:\\” *\/\\n if(curlx_dyn_addn(binding, prefix, sizeof(prefix) – 1) != CURLE_OK)\\n return CURLE_OUT_OF_MEMORY;\\n \/* Append digest *\/\\n if(curlx_dyn_addn(binding, buf, length))\\n return CURLE_OUT_OF_MEMORY;\\n\\n return CURLE_OK;\\n\\n\\nStatement on AI usage: AI was used in parts of detection, triage, fix generation and reporting writing in combination with classical tooling and manual human input.\\n\\n## Impact\\n\\n## Impact\\n\\nA remote HTTPS server that advertises `WWW-Authenticate: Negotiate` can cause a libcurl client (built with OpenSSL and GSSAPI) to leak one X509 certificate reference per authentication attempt when TLS channel binding is retrieved.\\n\\nOver many requests in a long-lived process, this leads to unbounded memory growth and a denial-of-service condition due to resource exhaustion.\\n\\nThe leak occurs because `ossl_get_channel_binding` calls `SSL_get1_peer_certificate` (which increments the X509 reference count) but never calls `X509_free` on any return path\u2014success or error.\\n\\n### Constraints:\\n- Requires libcurl built with OpenSSL (\\u003e=1.1.0) and GSSAPI support\\n- Only affects clients using Negotiate authentication over HTTPS\\n- Linear leak rate (not amplified), but unbounded over time\\n\\nSeverity: **Low** (limited scope, requires specific build configuration and authentication method, but genuine DoS risk for affected deployments)”,”published”:”2025-10-06T21:39:14″,”modified”:”2025-10-08T06:38:54″,”type”:”hackerone”,”title”:”curl: OpenSSL backend: X509 peer certificate not freed in ossl_get_channel_binding causes per-request memory leak (DoS risk for long-lived clients)”,”source”:””,”references”:””,”id”:”H1:3373640″,”bulletinFamily”:”bugbounty”,”cwe”:null,”cvelist”:[],”sourceData”:””,”sourceHref”:””,”cvss”:{“score”:0,”severity”:”NONE”,”vector”:”NONE”,”version”:”NONE”},”cvss2″:{},”cvss3″:{“version”:””,”vectorString”:””,”baseScore”:0,”baseSeverity”:””,”attackVector”:””,”attackComplexity”:””,”privilegesRequired”:””,”userInteraction”:””,”scope”:””,”confidentialityImpact”:””,”integrityImpact”:””,”availabilityImpact”:””,”cvssV3″:{“version”:””,”vectorString”:””,”baseScore”:0,”baseSeverity”:””,”attackVector”:””,”attackComplexity”:””,”privilegesRequired”:””,”userInteraction”:””,”scope”:””,”confidentialityImpact”:””,”integrityImpact”:””,”availabilityImpact”:””}},”href”:”https:\/\/hackerone.com\/reports\/3373640″,”category_name”:”News”,”post_link”:””,”product”:””,”version”:””,”vendor”:””,”ai_description”:””,”ai_severity”:””,”ai_vendor”:””,”ai_product”:””,”ai_version”:””,”ai_score”:0}<\/p>\n","protected":false},"excerpt":{"rendered":"
{“lastseen”:”2025-10-08T07:25:45″,”description”:”## Summary:\\nIn curl\u2019s OpenSSL backend, `ossl_get_channel_binding` retains a new reference to the server\u2019s X509 certificate via `SSL_get1_peer_certificate` and never releases it. When Negotiate (SPNEGO) over…<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[4],"tags":[6,8,12,117,13,33,7,11,5],"class_list":["post-20630","post","type-post","status-publish","format-standard","hentry","category-category_news","tag-cve","tag-cvss","tag-exploit","tag-hackerone","tag-news","tag-none","tag-security","tag-tapic","tag-vulnerability"],"yoast_head":"\n