CVE-2021-47515: seg6: fix the iif in the IPv6 socket control block
Vulnerability summary
CVE-2021-47515 is a high (CVSS 7.5) NULL Pointer Dereference vulnerability in linux. EPSS estimates a 0.75% chance of exploitation in the next 30 days, higher than 54.8% of scored vulnerabilities.
Severe, CVSS 7.5 (CVE.org); no exploitation reported by the 5 checked sources; EPSS 1% (FIRST, 03-11-2026)
Source freshness unavailable
How is this decided?Advisory lineage
Upstream 0 · Downstream 4 · Related 3Timeline
- 24-05-2024PublishedVulnerability first disclosed.
- 05-08-2026Last modifiedVulnerability information updated.
Description
In the Linux kernel, the following vulnerability has been resolved: seg6: fix the iif in the IPv6 socket control block When an IPv4 packet is received, the ip_rcv_core(...) sets the receiving interface index into the IPv4 socket control block (v5.16-rc4, net/ipv4/ip_input.c line 510): IPCB(skb)->iif = skb->skb_iif; If that IPv4 packet is meant to be encapsulated in an outer IPv6+SRH header, the seg6_do_srh_encap(...) performs the required encapsulation. In this case, the seg6_do_srh_encap function clears the IPv6 socket control block (v5.16-rc4 net/ipv6/seg6_iptunnel.c line 163): memset(IP6CB(skb), 0, sizeof(*IP6CB(skb))); The memset(...) was introduced in commit ef489749aae5 ("ipv6: sr: clear IP6CB(skb) on SRH ip4ip6 encapsulation") a long time ago (2019-01-29). Since the IPv6 socket control block and the IPv4 socket control block share the same memory area (skb->cb), the receiving interface index info is lost (IP6CB(skb)->iif is set to zero). As a side effect, that condition triggers a NULL pointer dereference if commit 0857d6f8c759 ("ipv6: When forwarding count rx stats on the orig netdev") is applied. To fix that issue, we set the IP6CB(skb)->iif with the index of the receiving interface once again.
CVSS metrics
5 scores · 4 sources · 2 versions- OSV · UbuntuEcosystem advisory · calculated7.5HighCVSS:3.1/AV:N/AC:L/PR:N/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:HDiffers
- NVDNIST5.5MediumCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:HDiffers
EPSS trend
Probability
0.75%
Chance of exploitation in the next 30 days
Percentile
55%
Versus all other CVEs
30-day change
No change 0.00 pp
From 0.75% 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: network-reachable, no authentication, no user interaction (CVSS vector). Other conditions: not stated in public data.
Ubuntu87 products
- linux< 4.15.0-169.177 | < 5.4.0-100.113
- linux-allwinner-5.19All versions (No fix recorded)
- linux-aws< 4.15.0-1121.129 | < 5.4.0-1066.69
- linux-aws-5.0All versions (No fix recorded)
- linux-aws-5.11All versions (No fix recorded)
Linux2 products
- linux≥ c630ec8bdadae9d557b1ceb9d6c06e149108a0d4, < b16d412e5f79734033df04e97d7ea2f50a8e9fe3 | ≥ 2f704348c93ff8119e642dae6a72327f90b82810, < 6431e71093f3da586a00c6d931481ffb0dc2db0e | ≥ ef489749aae508e6f17886775c075f12ff919fb1, < ef8804e47c0a44ae106ead1740408af5ea6c6ee9 | ≥ ef489749aae508e6f17886775c075f12ff919fb1, < 666521b3852d2b2f52d570f9122b1e4b50d96831 | ≥ ef489749aae508e6f17886775c075f12ff919fb1, < 98adb2bbfa407c9290bda299d4c6f7a1c4ebd5e1 | ≥ ef489749aae508e6f17886775c075f12ff919fb1, < ae68d93354e5bf5191ee673982251864ea24dd5c | b71b7e0280f47b4ac633fbfd153423814ea87810 | ≥ 4.14.98, < 4.14.258 | ≥ 4.19.20, < 4.19.221 | ≥ 4.20.7, < 4.21 | 5.0
- linux_kernel≥ 4.14.98, < 4.14.258 | ≥ 4.19.20, < 4.19.221 | ≥ 4.20.7, < 5.0 | ≥ 5.0.1, < 5.4.165 | ≥ 5.5, < 5.10.85 | ≥ 5.11, < 5.15.8 | 5.0 | 5.0:rc6 | 5.0:rc7 | 5.0:rc8 | 5.16:rc1 | 5.16:rc2 | 5.16:rc3 | 5.16:rc4
Debian1 product
- linux< 5.15.15-1
3 vendors · 90 products
