{"id":"CVE-2026-89720","state":"PUBLISHED","title":"ubifs: fix out-of-bounds read in signature length check","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nubifs: fix out-of-bounds read in signature length check\n\nubifs_sb_verify_signature() bounds the on-disk ubifs_sig_node->len field\nbefore handing the signature payload to verify_pkcs7_signature(), but the\ncheck has the wrong sign:\n\n\tif (le32_to_cpu(signode->len) > snod->len + sizeof(struct ubifs_sig_node))\n\nThe signature bytes start sizeof(struct ubifs_sig_node) (UBIFS_SIG_NODE_SZ,\n64 bytes) into the node, so the payload is at most\n\n\tsnod->len - sizeof(struct ubifs_sig_node)\n\nbytes long. Adding the header size instead of subtracting it accepts a\ndeclared length up to 2 * UBIFS_SIG_NODE_SZ larger than the node actually\nholds -- past the end of c->sbuf, which is vmalloc(c->leb_size).\nverify_pkcs7_signature() -> pkcs7_parse_message() -> asn1_ber_decoder()\nis then handed that inflated length and reads beyond the allocation while\nwalking the DER headers. The node length comes straight from the mounted\nimage, so a crafted signed UBIFS image reaches this via\nubifs_read_superblock() before the signature is cryptographically checked.\n\nsnod->len is guaranteed to be >= UBIFS_SIG_NODE_SZ by the node scanner\n(c->ranges[UBIFS_SIG_NODE].min_len == UBIFS_SIG_NODE_SZ), so the corrected\nsubtraction cannot underflow. Legitimately signed images are unaffected: a\ncorrect superblock never declares a signature longer than the node it is\nembedded in.","publishedAt":"2026-09-11T19:46:32.923Z","updatedAt":"2026-10-19T08:51:33.033Z","severity":{"score":7.7,"label":"High","version":"3.1","vector":"CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H","source":"Linux"},"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"817aa094842dfc3a6b98c9582d4a647827f66201","status":"affected","lessThan":"ab7405bd86331cc2dbc8201699d4adc33bea75e7","versionType":"git"},{"version":"817aa094842dfc3a6b98c9582d4a647827f66201","status":"affected","lessThan":"11abc34698cb3172badf8aa12e623f1bac98bbd8","versionType":"git"},{"version":"817aa094842dfc3a6b98c9582d4a647827f66201","status":"affected","lessThan":"8cc3da72cf57acb4b77442ea8cec48425dff7c06","versionType":"git"},{"version":"817aa094842dfc3a6b98c9582d4a647827f66201","status":"affected","lessThan":"37a9d25a563f5f9103282954ce573c4a61321e7c","versionType":"git"},{"version":"817aa094842dfc3a6b98c9582d4a647827f66201","status":"affected","lessThan":"f76b79d6e42af20682495bccd22f72c7164b0018","versionType":"git"},{"version":"817aa094842dfc3a6b98c9582d4a647827f66201","status":"affected","lessThan":"a1dc246f98bb94233effa4fa3ec7bf84700bb7d1","versionType":"git"},{"version":"817aa094842dfc3a6b98c9582d4a647827f66201","status":"affected","lessThan":"83e1aa9f5f906c9b1f4949d0521f0f950a159d96","versionType":"git"},{"version":"817aa094842dfc3a6b98c9582d4a647827f66201","status":"affected","lessThan":"95d27c1708bb6e8823c8e7c623f9abc2a91bf4bf","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/ubifs/auth.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"5.3","status":"affected"},{"version":"0","status":"unaffected","lessThan":"5.3","versionType":"semver"},{"version":"5.10.270","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.15.221","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"6.1.188","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.157","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.109","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.50","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.2.4","status":"unaffected","lessThanOrEqual":"7.2.*","versionType":"semver"},{"version":"7.3","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/ubifs/auth.c"]}],"references":["https://git.kernel.org/stable/c/ab7405bd86331cc2dbc8201699d4adc33bea75e7","https://git.kernel.org/stable/c/11abc34698cb3172badf8aa12e623f1bac98bbd8","https://git.kernel.org/stable/c/8cc3da72cf57acb4b77442ea8cec48425dff7c06","https://git.kernel.org/stable/c/37a9d25a563f5f9103282954ce573c4a61321e7c","https://git.kernel.org/stable/c/f76b79d6e42af20682495bccd22f72c7164b0018","https://git.kernel.org/stable/c/a1dc246f98bb94233effa4fa3ec7bf84700bb7d1","https://git.kernel.org/stable/c/83e1aa9f5f906c9b1f4949d0521f0f950a159d96","https://git.kernel.org/stable/c/95d27c1708bb6e8823c8e7c623f9abc2a91bf4bf"],"weaknesses":[],"ingestedAt":"2026-10-29T20:13:26.108Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/89xxx/CVE-2026-89720.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-89720","state":"PUBLISHED","datePublished":"2026-09-11T19:46:32.923Z","dateUpdated":"2026-10-19T08:51:33.033Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2026-09-11T19:38:34.752Z"},"containers":{"cna":{"title":"ubifs: fix out-of-bounds read in signature length check","descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nubifs: fix out-of-bounds read in signature length check\n\nubifs_sb_verify_signature() bounds the on-disk ubifs_sig_node->len field\nbefore handing the signature payload to verify_pkcs7_signature(), but the\ncheck has the wrong sign:\n\n\tif (le32_to_cpu(signode->len) > snod->len + sizeof(struct ubifs_sig_node))\n\nThe signature bytes start sizeof(struct ubifs_sig_node) (UBIFS_SIG_NODE_SZ,\n64 bytes) into the node, so the payload is at most\n\n\tsnod->len - sizeof(struct ubifs_sig_node)\n\nbytes long. Adding the header size instead of subtracting it accepts a\ndeclared length up to 2 * UBIFS_SIG_NODE_SZ larger than the node actually\nholds -- past the end of c->sbuf, which is vmalloc(c->leb_size).\nverify_pkcs7_signature() -> pkcs7_parse_message() -> asn1_ber_decoder()\nis then handed that inflated length and reads beyond the allocation while\nwalking the DER headers. The node length comes straight from the mounted\nimage, so a crafted signed UBIFS image reaches this via\nubifs_read_superblock() before the signature is cryptographically checked.\n\nsnod->len is guaranteed to be >= UBIFS_SIG_NODE_SZ by the node scanner\n(c->ranges[UBIFS_SIG_NODE].min_len == UBIFS_SIG_NODE_SZ), so the corrected\nsubtraction cannot underflow. Legitimately signed images are unaffected: a\ncorrect superblock never declares a signature longer than the node it is\nembedded in."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"817aa094842dfc3a6b98c9582d4a647827f66201","status":"affected","lessThan":"ab7405bd86331cc2dbc8201699d4adc33bea75e7","versionType":"git"},{"version":"817aa094842dfc3a6b98c9582d4a647827f66201","status":"affected","lessThan":"11abc34698cb3172badf8aa12e623f1bac98bbd8","versionType":"git"},{"version":"817aa094842dfc3a6b98c9582d4a647827f66201","status":"affected","lessThan":"8cc3da72cf57acb4b77442ea8cec48425dff7c06","versionType":"git"},{"version":"817aa094842dfc3a6b98c9582d4a647827f66201","status":"affected","lessThan":"37a9d25a563f5f9103282954ce573c4a61321e7c","versionType":"git"},{"version":"817aa094842dfc3a6b98c9582d4a647827f66201","status":"affected","lessThan":"f76b79d6e42af20682495bccd22f72c7164b0018","versionType":"git"},{"version":"817aa094842dfc3a6b98c9582d4a647827f66201","status":"affected","lessThan":"a1dc246f98bb94233effa4fa3ec7bf84700bb7d1","versionType":"git"},{"version":"817aa094842dfc3a6b98c9582d4a647827f66201","status":"affected","lessThan":"83e1aa9f5f906c9b1f4949d0521f0f950a159d96","versionType":"git"},{"version":"817aa094842dfc3a6b98c9582d4a647827f66201","status":"affected","lessThan":"95d27c1708bb6e8823c8e7c623f9abc2a91bf4bf","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/ubifs/auth.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"5.3","status":"affected"},{"version":"0","status":"unaffected","lessThan":"5.3","versionType":"semver"},{"version":"5.10.270","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.15.221","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"6.1.188","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.157","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.109","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.18.50","status":"unaffected","lessThanOrEqual":"6.18.*","versionType":"semver"},{"version":"7.2.4","status":"unaffected","lessThanOrEqual":"7.2.*","versionType":"semver"},{"version":"7.3","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["fs/ubifs/auth.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/ab7405bd86331cc2dbc8201699d4adc33bea75e7"},{"url":"https://git.kernel.org/stable/c/11abc34698cb3172badf8aa12e623f1bac98bbd8"},{"url":"https://git.kernel.org/stable/c/8cc3da72cf57acb4b77442ea8cec48425dff7c06"},{"url":"https://git.kernel.org/stable/c/37a9d25a563f5f9103282954ce573c4a61321e7c"},{"url":"https://git.kernel.org/stable/c/f76b79d6e42af20682495bccd22f72c7164b0018"},{"url":"https://git.kernel.org/stable/c/a1dc246f98bb94233effa4fa3ec7bf84700bb7d1"},{"url":"https://git.kernel.org/stable/c/83e1aa9f5f906c9b1f4949d0521f0f950a159d96"},{"url":"https://git.kernel.org/stable/c/95d27c1708bb6e8823c8e7c623f9abc2a91bf4bf"}],"metrics":[{"cvssV3_1":{"version":"3.1","vectorString":"CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H","baseScore":7.7,"baseSeverity":"HIGH"},"scenarios":[{"lang":"en","value":"AV:L - The OOB read is reached only while mounting a local UBIFS/UBI volume (mount → ubifs_fill_super → mount_ubifs → ubifs_read_superblock → authenticate_sb_node → ubifs_sb_verify_signature). The inflated ubifs_sig_node->len comes from on-disk flash, not ksmbd, nfsd, or any received-packet path.\nAC:L - The attacker fully controls the on-disk SIG node size and signode->len. The inverted check accepts a payload up to snod->len+64; with a node filling the LEB that deterministically reads 128 bytes past vmalloc'd c->sbuf in asn1_ber_decoder(), with no race or uncontrolled layout.\nPR:N - Supplying the crafted authenticated image needs no account on the victim. ubifs_fs_type lacks FS_USERNS_MOUNT, so the CAP_SYS_ADMIN mount (boot-time auth_key mount on embedded, automotive, and IoT devices that use offline-signed UBIFS) is performed by the platform, matching the malicious-filesystem model.\nUI:N - Offline-signed UBIFS is verified automatically at mount; boot/fstab auto-mount with auth_key runs ubifs_sb_verify_signature in ubifs_read_superblock before any file access, so planting or presenting the crafted volume is sufficient with no separate victim click or open.\nS:U - The out-of-bounds read and any oops remain inside the mounting host kernel. This is a same-authority memory-safety issue, not a VM escape, IOMMU bypass, or other cross-boundary impact.\nC:H - verify_pkcs7_signature() → pkcs7_parse_message() → asn1_ber_decoder() walks an attacker-inflated length of up to 128 bytes past c->sbuf (vmalloc of the LEB). That is an out-of-bounds kernel read of adjacent vmalloc memory, which is Confidentiality High rather than a few-byte leak.\nI:N - The defect is an out-of-bounds read of PKCS#7/ASN.1 headers; the decoder copies those bytes only into newly allocated parse objects sized from the claimed length and does not write past any allocation or provide an arbitrary-write or control-flow primitive.\nA:H - Reading past the vmalloc LEB buffer into an unmapped vmalloc guard page oopses or panics the kernel during mount, and a crafted image can retrigger that crash on every boot or mount of the volume."}]}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-10-19T08:51:33.033Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.3","versionEndExcluding":"5.10.270"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.3","versionEndExcluding":"5.15.221"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.3","versionEndExcluding":"6.1.188"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.3","versionEndExcluding":"6.6.157"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.3","versionEndExcluding":"6.12.109"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.3","versionEndExcluding":"6.18.50"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.3","versionEndExcluding":"7.2.4"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"5.3","versionEndExcluding":"7.3"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}}}}}