CVE-2021-46904: net: hso: fix null-ptr-deref during tty device unregistration
Vulnerability summary
CVE-2021-46904 is a medium (CVSS 5.5) NULL Pointer Dereference vulnerability in linux. EPSS estimates a 0.26% chance of exploitation in the next 30 days, higher than 17.2% of scored vulnerabilities.
Not severe (CVSS 5.5, local access); no exploitation reported by the 5 checked sources
Source freshness unavailable
How is this decided?Advisory lineage
Upstream 0 · Downstream 9 · Related 9Timeline
- 25-02-2024PublishedVulnerability first disclosed.
- 11-05-2026Last modifiedVulnerability information updated.
Description
In the Linux kernel, the following vulnerability has been resolved: net: hso: fix null-ptr-deref during tty device unregistration Multiple ttys try to claim the same the minor number causing a double unregistration of the same device. The first unregistration succeeds but the next one results in a null-ptr-deref. The get_free_serial_index() function returns an available minor number but doesn't assign it immediately. The assignment is done by the caller later. But before this assignment, calls to get_free_serial_index() would return the same minor number. Fix this by modifying get_free_serial_index to assign the minor number immediately after one is found to be and rename it to obtain_minor() to better reflect what it does. Similary, rename set_serial_by_index() to release_minor() and modify it to free up the minor number of the given hso_serial. Every obtain_minor() should have corresponding release_minor() call.
CVSS metrics
4 scores · 3 sources · 2 versions- OSV · UbuntuEcosystem advisory · calculated5.5MediumCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
- OSV · DebianEcosystem advisory · calculated5.5MediumCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
EPSS trend
Probability
0.26%
Chance of exploitation in the next 30 days
Percentile
17%
Versus all other CVEs
30-day change
No change 0.00 pp
From 0.26% on 04-10-2026
Known exploited
Compare KEV catalogs
CISA KEVNot in the CISA KEV catalog.
ENISA CNWNot in the ENISA CNW catalog.
CIRCLNot in the CIRCL catalog.
Public exploits
0 foundNo public exploits indexed.
Weaknesses
CWE · root causeAffected systems
Known conditions: local access, low-privilege account, no user interaction (CVSS vector). Other conditions: not stated in public data.
Ubuntu86 products
- linux< 3.13.0-199.250 | < 4.4.0-258.292 | < 4.15.0-144.148 | < 5.4.0-74.83
- linux-allwinner-5.19All versions (No fix recorded)
- linux-aws< 4.4.0-1135.141 | < 4.4.0-1173.188 | < 4.15.0-1103.110 | < 5.4.0-1049.51
- linux-aws-5.0All versions (No fix recorded)
- linux-aws-5.11All versions (No fix recorded)
Linux2 products
- linux≥ 72dc1c096c7051a48ab1dbb12f71976656b55eb5, < a462067d7c8e6953a733bf5ade8db947b1bb5449 | ≥ 72dc1c096c7051a48ab1dbb12f71976656b55eb5, < 145c89c441d27696961752bf51b323f347601bee | ≥ 72dc1c096c7051a48ab1dbb12f71976656b55eb5, < caf5ac93b3b5d5fac032fc11fbea680e115421b4 | ≥ 72dc1c096c7051a48ab1dbb12f71976656b55eb5, < 92028d7a31e55d53e41cff679156b9432cffcb36 | ≥ 72dc1c096c7051a48ab1dbb12f71976656b55eb5, < 4a2933c88399c0ebc738db39bbce3ae89786d723 | ≥ 72dc1c096c7051a48ab1dbb12f71976656b55eb5, < dc195928d7e4ec7b5cfc6cd10dc4c8d87a7c72ac | ≥ 72dc1c096c7051a48ab1dbb12f71976656b55eb5, < 388d05f70f1ee0cac4a2068fd295072f1a44152a | ≥ 72dc1c096c7051a48ab1dbb12f71976656b55eb5, < 8a12f8836145ffe37e9c8733dce18c22fb668b66 | 2.6.27
- linux_kernel≥ 2.6.27, < 4.4.268 | ≥ 4.5.0, < 4.9.268 | ≥ 4.10.0, < 4.14.232 | ≥ 4.15.0, < 4.19.187 | ≥ 4.20.0, < 5.4.112 | ≥ 5.5.0, < 5.10.30 | ≥ 5.11.0, < 5.11.14
Debian1 product
- linux< 5.10.38-1
3 vendors · 89 products
