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CVE-2026-74583— net/sched: cls_route: fix fastmap use-after-free on filter

Quick assessment

Affected
Linux Linux
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

Linux kernel是美国Linux基金会开源的一个操作系统内核。 Linux kernel 3.18版本存在安全漏洞，该漏洞源于route4分类器fastmap缓存处理存在释放后重用竞争条件，可能导致攻击者读取已释放内存。

CVSS 7.8 · High EPSS 0.12% · P2

Possible ATT&CK Techniques 1 AI

T1190 · Exploit Public-Facing Application

Affected Version Matrix 18

VendorProduct Version RangeStatus
Linux Linux 1109c00547fc66df45b9ff923544be4c1e1bec13< 7897198b26445b4009a057bda1986b94a99e5d5f affected
1109c00547fc66df45b9ff923544be4c1e1bec13< 820f083c294ad6d319c02a7d43294f2ed2565139 affected
1109c00547fc66df45b9ff923544be4c1e1bec13< 5ec9001be6d0eb527251125632ec8fe88278897f affected
1109c00547fc66df45b9ff923544be4c1e1bec13< b969984b2bdc85d721ce4047cd270cd37ec705a2 affected
1109c00547fc66df45b9ff923544be4c1e1bec13< a17f636c9330eac879822ce29f998e5abd1b72c1 affected
1109c00547fc66df45b9ff923544be4c1e1bec13< 0e7a8cf8895b06d07c7311f028eba16ad742b9bc affected
1109c00547fc66df45b9ff923544be4c1e1bec13< ae9aff87025219005a2d16b4fe83d6f24643e50d affected
1109c00547fc66df45b9ff923544be4c1e1bec13< 47d7f7051253bdc02b1d245d87e38f16d31a74df affected
… +10 more rows
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I. Basic Information for CVE-2026-74583

Vulnerability Information
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Vulnerability Title
net/sched: cls_route: fix fastmap use-after-free on filter
Source: CVE Program / CVE List V5
Vulnerability Description
In the Linux kernel, the following vulnerability has been resolved: net/sched: cls_route: fix fastmap use-after-free on filter The route4 classifier maintains a 16-slot fastmap cache that stores raw struct route4_filter pointers indexed by (id, iif). The reader (route4_classify) populates this cache via route4_set_fastmap() for every classified packet that hits a filter. The writer (route4_delete, route4_change) clears the cache via route4_reset_fastmap() before RCU-deferred kfree of the filter. This creates a UAF race: 1. Reader walks the RCU-protected bucket chain, finds filter f 2. Writer unlinks f, calls route4_reset_fastmap(), then tcf_queue_work() 3. Reader calls route4_set_fastmap() and writes f into the cache *after* the writer's reset, caching a pointer about to be freed 4. After the RCU grace period, kfree(f) executes 5. Next classified packet on the same (id, iif) tuple hits the stale fastmap entry and reads f->res from freed memory Reproduced with an mdelay(100) accelerator in route4_set_fastmap() and a concurrent add/delete stress test (provided by both zdi and Santosh). Both triggered KASAN slab-use-after-free reports in the route4 fastmap paths. Fix: Introduce a per-filter boolean dying flag to suppress stale fastmap republishing by in-flight readers.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
N/A
Source: CVE Program / CVE List V5
Vulnerability Title
Linux kernel 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Linux kernel是美国Linux基金会开源的一个操作系统内核。 Linux kernel 3.18版本存在安全漏洞，该漏洞源于route4分类器fastmap缓存处理存在释放后重用竞争条件，可能导致攻击者读取已释放内存。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

Vendor Product Affected Versions CPE Subscribe
Linux Linux 1109c00547fc66df45b9ff923544be4c1e1bec13 ~ 7897198b26445b4009a057bda1986b94a99e5d5f -
Linux Linux 3.18 -

II. Public POCs for CVE-2026-74583

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III. Intelligence Information for CVE-2026-74583

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Patches & Fixes for CVE-2026-74583 (8)

Same Patch Batch · Linux · 2026-08-21 · 4 CVEs total

CVE-2026-74581 9.8 CRITICAL net: ipv6: clear suppressed fib6 rule result
CVE-2026-74580 8.8 HIGH vhost: reset the vring metadata cache on vring reconfiguration
CVE-2026-74582 7.8 HIGH packet: use consistent hard_header_len in non-ring send paths

IV. Related Vulnerabilities

Same product: Linux
Same vendor: Linux

V. Comments for CVE-2026-74583

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