{"id":"CVE-2026-46300","kind":"vulnerability","aliases":["CVE-2026-46300"],"related":[],"title":"In the Linux kernel, the following vulnerability has been resolved: net: skbuff: preserve shared-frag marker during…","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nnet: skbuff: preserve shared-frag marker during coalescing\n\nskb_try_coalesce() can attach paged frags from @from to @to.  If @from\nhas SKBFL_SHARED_FRAG set, the resulting @to skb can contain the same\nexternally-owned or page-cache-backed frags, but the shared-frag marker\nis currently lost.\n\nThat breaks the invariant relied on by later in-place writers.  In\nparticular, ESP input checks skb_has_shared_frag() before deciding\nwhether an uncloned nonlinear skb can skip skb_cow_data().  If TCP\nreceive coalescing has moved shared frags into an unmarked skb, ESP can\nsee skb_has_shared_frag() as false and decrypt in place over page-cache\nbacked frags.\n\nPropagate SKBFL_SHARED_FRAG when skb_try_coalesce() transfers paged\nfrags.  The tailroom copy path does not need the marker because it copies\nbytes into @to's linear data rather than transferring frag descriptors.","summary":"A missing variable initialization in the Linux kernel's socket buffer coalescing drops the shared-fragment marker, so ESP input processing can decrypt shared page-cache fragments in place. An attacker can modify cached file data and, per CISA's notice, chain it with two other flaws to plant PHP webshells and run commands as root.","severity":"high","cvss":7.8,"epss":0.10192,"exploited":true,"exploited_at":"2026-10-28T00:00:00+00:00","products":[{"name":"linux kernel","fixed":[],"affected":">= 3.9, <= 5.10.257","ecosystem":"vendor"},{"name":"linux kernel","fixed":["5.15.208"],"affected":">= 5.11, < 5.15.208","ecosystem":"vendor"},{"name":"linux kernel","fixed":["6.1.174"],"affected":">= 5.16, < 6.1.174","ecosystem":"vendor"},{"name":"linux kernel","fixed":["6.6.141"],"affected":">= 6.2, < 6.6.141","ecosystem":"vendor"},{"name":"linux kernel","fixed":["6.12.91"],"affected":">= 6.7, < 6.12.91","ecosystem":"vendor"},{"name":"linux kernel","fixed":["6.18.33"],"affected":">= 6.13, < 6.18.33","ecosystem":"vendor"},{"name":"linux kernel","fixed":["7.0.10"],"affected":">= 6.19, < 7.0.10","ecosystem":"vendor"},{"name":"linux kernel","fixed":[],"affected":"= 7.1","ecosystem":"vendor"},{"name":"Linux Kernel","fixed":[],"affected":"","ecosystem":"vendor"}],"ecosystems":["vendor"],"tags":["exploited","infrastructure","ipsec","linux-kernel","self-hosted"],"not_affected_if":["default-config"],"how_to_check":"- unknown","fix":"- Apply the kernel update from your distribution that includes the fix for CVE-2026-46300, per vendor instructions.\n- If no fix is available, follow CISA BOD 26-04 guidance or stop using the affected product.","status":"open","published_at":"2026-05-23T12:17:02+00:00","first_seen_at":"2026-10-28T20:01:38+00:00","triaged_at":"2026-10-28T20:02:52+00:00","updated_at":"2026-10-28T21:01:52+00:00","category":"infrastructure","confidence":0.5,"triage":{"at":"2026-10-28T20:02:52Z","model":"claude-haiku-5-5","output":{"fix":"- Apply the kernel update from your distribution that includes the fix for CVE-2026-46300, per vendor instructions.\n- If no fix is available, follow CISA BOD 26-04 guidance or stop using the affected product.","reach":"unknown","title":"Linux kernel: ESP coalescing flaw lets attackers modify page-cache data","impact":"high","summary":"A missing variable initialization in the Linux kernel's socket buffer coalescing drops the shared-fragment marker, so ESP input processing can decrypt shared page-cache fragments in place. An attacker can modify cached file data and, per CISA's notice, chain it with two other flaws to plant PHP webshells and run commands as root.","category":"infrastructure","nicknames":[],"who_cares":["linux-kernel","self-hosted","ipsec"],"confidence":0.5,"needs_auth":"unknown","worst_case":"Attacker modifies cached file data and escalates to root.","analyst_note":"Find the affected and fixed kernel versions and the ESP trigger conditions in the CISA KEV entry and vendor advisories; the description links to CVE-2026-109618 and CVE-2026-109619 which should be checked.","how_to_check":"- unknown","needs_analyst":true,"not_affected_if":["default-config"],"who_is_affected":"Systems running a Linux kernel with IPsec ESP processing that has not received the fix. Hosts that do not use ESP (IPsec) are less likely exposed, but the sources do not confirm a specific configuration requirement. Exposure of internet-facing servers should be evaluated per BOD 26-04.","user_interaction":"unknown","needs_special_setup":"unknown","severity_if_unknown":"high"},"cost_usd":0.000655,"input_tokens":3578,"output_tokens":594,"severity_before":"unknown"},"analyst_status":null,"analyst_note":null,"search":"'-2026':19A,22A '-46300':20A,23A 'attach':132C 'attack':83B 'back':161C,234C 'break':173C 'buffer':61B 'byte':259C 'cach':78B,86B,160C,233C 'chain':94B 'check':188C 'cisa':91B 'coalesc':62B,127C,130C,208C,243C 'command':106B 'contain':151C 'copi':249C,258C 'cow':203C 'current':170C 'cve':18A,21A 'data':88B,204C,264C 'decid':194C 'decrypt':74B,227C 'descriptor':269C 'drop':63B 'esp':70B,186C,217C 'exploit':42B 'extern':155C 'externally-own':154C 'fals':225C 'file':87B 'flaw':99B 'follow':6A,114C 'frag':16A,124C,134C,144C,162C,167C,192C,212C,223C,235C,239C,246C,268C 'fragment':67B,79B 'host':50B 'in-plac':180C 'infrastructur':43B 'initi':54B 'input':71B,187C 'invari':175C 'ipsec':44B 'kernel':4A,25A,27A,29A,31A,33A,35A,37A,39A,41A,47B,58B,112C 'later':179C 'linear':263C 'linux':3A,24A,26A,28A,30A,32A,34A,36A,38A,40A,46B,57B,111C 'linux-kernel':45B 'lost':171C 'marker':17A,68B,125C,168C,255C 'miss':52B 'modifi':85B 'move':210C 'need':253C 'net':11A,119C 'nonlinear':198C 'notic':93B 'own':156C 'page':77B,133C,159C,232C,245C 'page-cach':76B,231C 'page-cache-back':158C 'particular':185C 'path':250C 'per':90B 'php':102B 'place':81B,182C,229C 'plant':101B 'preserv':13A,121C 'process':72B 'propag':236C 'rather':265C 'receiv':207C 'reli':176C 'resolv':10A,118C 'result':147C 'root':108B 'run':105B 'see':219C 'self':49B 'self-host':48B 'set':145C 'share':15A,66B,75B,123C,143C,166C,191C,211C,222C,238C 'shared-frag':14A,65B,122C,165C 'skb':128C,149C,189C,199C,202C,216C,220C,241C 'skbfl':142C,237C 'skbuff':12A,120C 'skip':201C 'socket':60B 'tailroom':248C 'tcp':206C 'transfer':244C,267C 'tri':129C,242C 'two':97B 'unclon':197C 'unmark':215C 'variabl':53B 'vulner':7A,115C 'webshel':103B 'whether':195C 'writer':183C","nicknames":[],"mitigations":[],"who_affected":"Systems running a Linux kernel with IPsec ESP processing that has not received the fix. Hosts that do not use ESP (IPsec) are less likely exposed, but the sources do not confirm a specific configuration requirement. Exposure of internet-facing servers should be evaluated per BOD 26-04.","tier":"A","verified":{},"analyst_revisit_at":null,"first_public_at":"2026-05-23T12:17:02+00:00","kev":{"dateAdded":"2026-10-28","dueDate":"2026-10-31","requiredAction":"Apply mitigations in accordance with vendor instructions, ensuring compliance with CISA’s BOD 26-04 Prioritizing Security Updates Based on Risk (see URL in Notes) guidance and CISA’s “Forensics Triage Requirements” (see URL in Notes). Follow applicable BOD 26-04 guidance for cloud services or discontinue use of the product if mitigations are unavailable. Stakeholders are responsible for evaluating each asset's internet exposure and ensuring adherence to BOD 26-04 patching guidelines.","knownRansomwareCampaignUse":"Unknown"},"cvss_vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","cvss_by":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","poc_count":0,"sources":[{"source":"kev","external_id":"CVE-2026-46300","url":"https://www.cisa.gov/known-exploited-vulnerabilities-catalog?search_api_fulltext=CVE-2026-46300","severity":null,"published_at":"2026-10-28T00:00:00+00:00","modified_at":null,"first_seen_at":"2026-10-28T20:01:38+00:00","fetched_at":"2026-10-28T21:01:52+00:00","note":null},{"source":"nvd","external_id":"CVE-2026-46300","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-46300","severity":null,"published_at":"2026-05-23T12:17:02+00:00","modified_at":"2026-10-19T20:18:40+00:00","first_seen_at":"2026-10-28T20:05:07+00:00","fetched_at":"2026-10-28T20:05:07+00:00","note":null},{"source":"epss","external_id":"CVE-2026-46300","url":"https://api.first.org/data/v1/epss?cve=CVE-2026-46300","severity":null,"published_at":null,"modified_at":null,"first_seen_at":"2026-10-28T20:59:22+00:00","fetched_at":"2026-10-28T20:59:22+00:00","note":null}],"documents":[],"notice":"Free to read at a human pace. An API with keys and an MCP server are in preparation; early access: hello@infrastack.ai"}