{"id":"CVE-2025-39766","state":"PUBLISHED","title":"net/sched: Make cake_enqueue return NET_XMIT_CN when past buffer_limit","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nnet/sched: Make cake_enqueue return NET_XMIT_CN when past buffer_limit\n\nThe following setup can trigger a WARNING in htb_activate due to\nthe condition: !cl->leaf.q->q.qlen\n\ntc qdisc del dev lo root\ntc qdisc add dev lo root handle 1: htb default 1\ntc class add dev lo parent 1: classid 1:1 \\\n       htb rate 64bit\ntc qdisc add dev lo parent 1:1 handle f: \\\n       cake memlimit 1b\nping -I lo -f -c1 -s64 -W0.001 127.0.0.1\n\nThis is because the low memlimit leads to a low buffer_limit, which\ncauses packet dropping. However, cake_enqueue still returns\nNET_XMIT_SUCCESS, causing htb_enqueue to call htb_activate with an\nempty child qdisc. We should return NET_XMIT_CN when packets are\ndropped from the same tin and flow.\n\nI do not believe return value of NET_XMIT_CN is necessary for packet\ndrops in the case of ack filtering, as that is meant to optimize\nperformance, not to signal congestion.","publishedAt":"2025-09-11T16:56:21.514Z","updatedAt":"2026-06-11T18:44:07.476Z","severity":null,"assigner":"Linux","products":["Linux Linux"],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"046f6fd5daefac7f5abdafb436b30f63bc7c602b","status":"affected","lessThan":"7689ab22de36f8db19095f6bdf11f28cfde92f5c","versionType":"git"},{"version":"046f6fd5daefac7f5abdafb436b30f63bc7c602b","status":"affected","lessThan":"de04ddd2980b48caa8d7e24a7db2742917a8b280","versionType":"git"},{"version":"046f6fd5daefac7f5abdafb436b30f63bc7c602b","status":"affected","lessThan":"0dacfc5372e314d1219f03e64dde3ab495a5a25e","versionType":"git"},{"version":"046f6fd5daefac7f5abdafb436b30f63bc7c602b","status":"affected","lessThan":"710866fc0a64eafcb8bacd91bcb1329eb7e5035f","versionType":"git"},{"version":"046f6fd5daefac7f5abdafb436b30f63bc7c602b","status":"affected","lessThan":"aa12ee1c1bd260943fd6ab556d8635811c332eeb","versionType":"git"},{"version":"046f6fd5daefac7f5abdafb436b30f63bc7c602b","status":"affected","lessThan":"ff57186b2cc39766672c4c0332323933e5faaa88","versionType":"git"},{"version":"046f6fd5daefac7f5abdafb436b30f63bc7c602b","status":"affected","lessThan":"62d591dde4defb1333d202410609c4ddeae060b3","versionType":"git"},{"version":"046f6fd5daefac7f5abdafb436b30f63bc7c602b","status":"affected","lessThan":"15de71d06a400f7fdc15bf377a2552b0ec437cf5","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/sched/sch_cake.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"4.19","status":"affected"},{"version":"0","status":"unaffected","lessThan":"4.19","versionType":"semver"},{"version":"5.4.297","status":"unaffected","lessThanOrEqual":"5.4.*","versionType":"semver"},{"version":"5.10.241","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.15.190","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"6.1.149","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.103","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.44","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.16.4","status":"unaffected","lessThanOrEqual":"6.16.*","versionType":"semver"},{"version":"6.17","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/sched/sch_cake.c"]}],"references":["https://git.kernel.org/stable/c/7689ab22de36f8db19095f6bdf11f28cfde92f5c","https://git.kernel.org/stable/c/de04ddd2980b48caa8d7e24a7db2742917a8b280","https://git.kernel.org/stable/c/0dacfc5372e314d1219f03e64dde3ab495a5a25e","https://git.kernel.org/stable/c/710866fc0a64eafcb8bacd91bcb1329eb7e5035f","https://git.kernel.org/stable/c/aa12ee1c1bd260943fd6ab556d8635811c332eeb","https://git.kernel.org/stable/c/ff57186b2cc39766672c4c0332323933e5faaa88","https://git.kernel.org/stable/c/62d591dde4defb1333d202410609c4ddeae060b3","https://git.kernel.org/stable/c/15de71d06a400f7fdc15bf377a2552b0ec437cf5","https://lists.debian.org/debian-lts-announce/2025/10/msg00008.html","https://lists.debian.org/debian-lts-announce/2025/10/msg00007.html","https://cert-portal.siemens.com/productcert/html/ssa-032379.html"],"weaknesses":[],"ingestedAt":"2026-10-29T20:09:09.358Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2025/39xxx/CVE-2025-39766.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2025-39766","state":"PUBLISHED","datePublished":"2025-09-11T16:56:21.514Z","dateUpdated":"2026-06-11T18:44:07.476Z","assignerShortName":"Linux","assignerOrgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateReserved":"2025-04-16T07:20:57.126Z"},"containers":{"cna":{"title":"net/sched: Make cake_enqueue return NET_XMIT_CN when past buffer_limit","descriptions":[{"lang":"en","value":"In the Linux kernel, the following vulnerability has been resolved:\n\nnet/sched: Make cake_enqueue return NET_XMIT_CN when past buffer_limit\n\nThe following setup can trigger a WARNING in htb_activate due to\nthe condition: !cl->leaf.q->q.qlen\n\ntc qdisc del dev lo root\ntc qdisc add dev lo root handle 1: htb default 1\ntc class add dev lo parent 1: classid 1:1 \\\n       htb rate 64bit\ntc qdisc add dev lo parent 1:1 handle f: \\\n       cake memlimit 1b\nping -I lo -f -c1 -s64 -W0.001 127.0.0.1\n\nThis is because the low memlimit leads to a low buffer_limit, which\ncauses packet dropping. However, cake_enqueue still returns\nNET_XMIT_SUCCESS, causing htb_enqueue to call htb_activate with an\nempty child qdisc. We should return NET_XMIT_CN when packets are\ndropped from the same tin and flow.\n\nI do not believe return value of NET_XMIT_CN is necessary for packet\ndrops in the case of ack filtering, as that is meant to optimize\nperformance, not to signal congestion."}],"affected":[{"vendor":"Linux","product":"Linux","defaultStatus":"unaffected","versions":[{"version":"046f6fd5daefac7f5abdafb436b30f63bc7c602b","status":"affected","lessThan":"7689ab22de36f8db19095f6bdf11f28cfde92f5c","versionType":"git"},{"version":"046f6fd5daefac7f5abdafb436b30f63bc7c602b","status":"affected","lessThan":"de04ddd2980b48caa8d7e24a7db2742917a8b280","versionType":"git"},{"version":"046f6fd5daefac7f5abdafb436b30f63bc7c602b","status":"affected","lessThan":"0dacfc5372e314d1219f03e64dde3ab495a5a25e","versionType":"git"},{"version":"046f6fd5daefac7f5abdafb436b30f63bc7c602b","status":"affected","lessThan":"710866fc0a64eafcb8bacd91bcb1329eb7e5035f","versionType":"git"},{"version":"046f6fd5daefac7f5abdafb436b30f63bc7c602b","status":"affected","lessThan":"aa12ee1c1bd260943fd6ab556d8635811c332eeb","versionType":"git"},{"version":"046f6fd5daefac7f5abdafb436b30f63bc7c602b","status":"affected","lessThan":"ff57186b2cc39766672c4c0332323933e5faaa88","versionType":"git"},{"version":"046f6fd5daefac7f5abdafb436b30f63bc7c602b","status":"affected","lessThan":"62d591dde4defb1333d202410609c4ddeae060b3","versionType":"git"},{"version":"046f6fd5daefac7f5abdafb436b30f63bc7c602b","status":"affected","lessThan":"15de71d06a400f7fdc15bf377a2552b0ec437cf5","versionType":"git"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/sched/sch_cake.c"]},{"vendor":"Linux","product":"Linux","defaultStatus":"affected","versions":[{"version":"4.19","status":"affected"},{"version":"0","status":"unaffected","lessThan":"4.19","versionType":"semver"},{"version":"5.4.297","status":"unaffected","lessThanOrEqual":"5.4.*","versionType":"semver"},{"version":"5.10.241","status":"unaffected","lessThanOrEqual":"5.10.*","versionType":"semver"},{"version":"5.15.190","status":"unaffected","lessThanOrEqual":"5.15.*","versionType":"semver"},{"version":"6.1.149","status":"unaffected","lessThanOrEqual":"6.1.*","versionType":"semver"},{"version":"6.6.103","status":"unaffected","lessThanOrEqual":"6.6.*","versionType":"semver"},{"version":"6.12.44","status":"unaffected","lessThanOrEqual":"6.12.*","versionType":"semver"},{"version":"6.16.4","status":"unaffected","lessThanOrEqual":"6.16.*","versionType":"semver"},{"version":"6.17","status":"unaffected","lessThanOrEqual":"*","versionType":"original_commit_for_fix"}],"repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","programFiles":["net/sched/sch_cake.c"]}],"references":[{"url":"https://git.kernel.org/stable/c/7689ab22de36f8db19095f6bdf11f28cfde92f5c"},{"url":"https://git.kernel.org/stable/c/de04ddd2980b48caa8d7e24a7db2742917a8b280"},{"url":"https://git.kernel.org/stable/c/0dacfc5372e314d1219f03e64dde3ab495a5a25e"},{"url":"https://git.kernel.org/stable/c/710866fc0a64eafcb8bacd91bcb1329eb7e5035f"},{"url":"https://git.kernel.org/stable/c/aa12ee1c1bd260943fd6ab556d8635811c332eeb"},{"url":"https://git.kernel.org/stable/c/ff57186b2cc39766672c4c0332323933e5faaa88"},{"url":"https://git.kernel.org/stable/c/62d591dde4defb1333d202410609c4ddeae060b3"},{"url":"https://git.kernel.org/stable/c/15de71d06a400f7fdc15bf377a2552b0ec437cf5"}],"providerMetadata":{"shortName":"Linux","orgId":"416baaa9-dc9f-4396-8d5f-8c081fb06d67","dateUpdated":"2026-05-11T21:35:50.638Z"},"cpeApplicability":[{"nodes":[{"operator":"OR","negate":false,"cpeMatch":[{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.19","versionEndExcluding":"5.4.297"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.19","versionEndExcluding":"5.10.241"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.19","versionEndExcluding":"5.15.190"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.19","versionEndExcluding":"6.1.149"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.19","versionEndExcluding":"6.6.103"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.19","versionEndExcluding":"6.12.44"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.19","versionEndExcluding":"6.16.4"},{"vulnerable":true,"criteria":"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*","versionStartIncluding":"4.19","versionEndExcluding":"6.17"}]}]}],"x_generator":{"engine":"bippy-1.2.0"}},"adp":[{"title":"CVE 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