A flaw in the processing of received ICMP errors (ICMP fragment needed and ICMP redirect) in the Linux kernel functionality was found to allow the ability to quickly scan open UDP ports. This flaw allows an off-path remote user to effectively bypass the source port UDP randomization. The highest threat from this vulnerability is to confidentiality and possibly integrity, because software that relies on UDP source port randomization are indirectly affected as well.
CVE-2021-20322
“—” beside the score: it is equal to NVD's CVSS score.
Score 7.4 from GitHub Security Advisory (severity: CRITICAL) published 2022-02-19. NVD baseline CVSS 7.4; sources differ by 0.0.
- High severity, but no confirmed exploitation yet
A fix is available — apply it.
- CVSS v3
- 7.4
- EG Score
- 7.4HIGHmedium confidence
- EG Risk
- 36EG Risk 36/100
EG Risk is EchelonGraph's 0–100 priority score. It fuses impact severity (EG Severity, the CVSS base score, never the KEV-floored or EPSS-lifted EG Score) with real-world exploitation and automatability, under weights EchelonGraph set by hand, so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner.
How it’s computed (value × EchelonGraph’s weight)Severity74% × 45%Impact severity (EG Severity): CVSS 7.4 of 10. Never the KEV-floored or EPSS-lifted EG Score.Exploitation6.9% × 40%FIRST EPSS: the 30-day exploitation probability when EchelonGraph scored this CVE.Automatability0% × 15%CISA's BOD 26-04 default: no one has published Automatable for this CVE, and CISA treats it as “no” for a CVE not in KEV.SSVC (CISA's decision table, applied by EchelonGraph): Track at low or medium mission impact; Track* at high (mission-essential systems).Exploitation none (no CISA value, KEV listing or exploit code on record) · Automatable no (CISA's BOD 26-04 default) · Technical impact total (CISA's BOD 26-04 default). EchelonGraph holds no SSVC assessment of this CVE from CISA: none of these inputs is from Vulnrichment. EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE.Action: A fix is available. Apply it within your standard update timelines. - EPSS PROB
- 6.9%
- EPSS %ILE
- 94th
- KEV
- Not listed
What the EG score is made of (scorer v4.0: the three questions the 0–10 score mixes, published apart · methodology)
The EG score (7.4): severity, escalated by confirmed exploitation. This CVE's 7.4 is its impact severity (EG Severity), not escalated.
- EG Severity
- 7.4 HIGHCVSS-B, impact only: no KEV listing, EPSS or EG-KEV tier raises it.GitHub Security Advisory CVSS
- EG Likelihood
- 6.9% within 30 daysSource: FIRST EPSS (model v2026.06.15, score date 2026-10-20). FIRST's exploitation probability, not an EchelonGraph model.
- Confirmed exploitation
- None on record (CISA KEV, EG-KEV Tier 1)Reported apart from the likelihood: an observed fact, not a probability.
- EG Priority
- SSVC Track at medium mission impactTrack at low or medium mission impact; Track* at high (mission-essential systems).CISA BOD 26-04: 14 days if the affected system is publicly exposed; Fix on system upgrade if it is not.Each input and its source: the SSVC and BOD 26-04 blocks below.
SSVC (CISA's decision table, applied by EchelonGraph)Track at low or medium mission impact; Track* at high (mission-essential systems).
A fix is available. Apply it within your standard update timelines.
Exploitation none (no CISA value, KEV listing or exploit code on record) · Automatable no (CISA's BOD 26-04 default) · Technical impact total (CISA's BOD 26-04 default). EchelonGraph holds no SSVC assessment of this CVE from CISA: none of these inputs is from Vulnrichment. EchelonGraph applied CISA's decision table to them; CISA publishes SSVC inputs and the table, not a decision for each CVE. Mission impact is CISA's Mission & Well-being decision point, and only you can judge it. CISA's table makes it high when Mission Prevalence is Essential — the vulnerable component "directly provides capabilities that constitute at least one MEF for at least one entity" (MEF: mission essential function) — or when Public Well-Being Impact is Irreversible: "multiple fatalities are likely", the cyber-physical system "is likely lost or destroyed", "extreme or serious externalities" are imposed on other parties, or social systems such as elections or the financial grid "are destabilized and potentially collapse". CISA's decision table
BOD 26-04 (CISA's remediation timeline, Table 1)14 days if the affected system is publicly exposed; Fix on system upgrade if it is not.
In CISA KEV no (CISA's KEV catalog) · Automatable no (CISA's BOD 26-04 default) · Technical impact total (CISA's BOD 26-04 default). Where an input reads “CISA's BOD 26-04 default”, no one has published it for this CVE, and CISA's implementation guidance says: “If “Automatable” and “Technical Impact” information items about a CVE ID are not available and the CVE ID is not in the KEV Catalog, CISA will treat its values as “no” and “total,” respectively, until CISA or a third party provides metadata about the CVE ID. CISA will always provide the Vulnrichment data for a CVE ID listed in the KEV Catalog.” Whether your system is publicly exposed is yours to answer. BOD 26-04 binds US Federal Civilian Executive Branch agencies; for anyone else it is CISA's published timeline, a reference rather than an obligation. The directive · how EchelonGraph applies it
Published
February 18, 2022
Last Modified
July 30, 2026
Advisory Details (8)
Auto-updated Jul 30, 2026[SECURITY] [DSA 5096-1] linux security update
https://www.debian.org/security/2022/dsa-5096[SECURITY] [DLA 2941-1] linux-4.19 security update
https://lists.debian.org/debian-lts-announce/2022/03/msg00012.htmlipv6: make exception cache less predictible - kernel/git/torvalds/linux.git - Linux kernel source tree
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/net/ipv6/route.c?h=v5.15-rc6&id=a00df2caffed3883c341d5685f830434312e4a43ipv4: make exception cache less predictible - kernel/git/torvalds/linux.git - Linux kernel source tree
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/net/ipv4/route.c?h=v5.15-rc6&id=67d6d681e15b578c1725bad8ad079e05d1c48a8eipv4: use siphash instead of Jenkins in fnhe_hashfun() - kernel/git/torvalds/linux.git - Linux kernel source tree
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?h=v5.15-rc6&id=6457378fe796815c973f631a1904e147d6ee33b1ipv6: use siphash in rt6_exception_hash() - kernel/git/torvalds/linux.git - Linux kernel source tree
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?h=v5.15-rc6&id=4785305c05b25a242e5314cc821f54ade4c188102014230 – (CVE-2021-20322) CVE-2021-20322 kernel: new DNS Cache Poisoning Attack based on ICMP fragment needed packets replies
Affected: Red Hat Enterprise Linux 8
https://bugzilla.redhat.com/show_bug.cgi?id=2014230Vendor Advisories for CVE-2021-20322(6)
These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.
- RHSA-2022:4835Red Hat Product SecurityHigh
Red Hat Security Advisory: kernel-rt security and bug fix update
- RHSA-2022:4829Red Hat Product SecurityHigh
Red Hat Security Advisory: kernel security, bug fix, and enhancement update
- RHSA-2022:1988Red Hat Product SecurityHigh
Red Hat Security Advisory: kernel security, bug fix, and enhancement update
- RHSA-2022:1975Red Hat Product SecurityHigh
Red Hat Security Advisory: kernel-rt security and bug fix update
- CVE-2021-20322Microsoft Security Response Center (MSRC)High
A flaw in the processing of received ICMP errors (ICMP fragment needed and ICMP redirect) in the Linux kernel functionality was found to allow the ability to quickly scan open UDP ports. This flaw allows an off-path remote user to effectively bypass the source port UDP randomization. The highest threat from this vulnerability is to confidentiality and possibly integrity because software that relies on UDP source port randomization are indirectly affected as well.
- GHSA-x37m-35qq-p254GitHub Security AdvisoriesCritical
A flaw in the processing of received ICMP errors (ICMP fragment needed and ICMP redirect) in the...
Patch Availability(5)
| Vendor / Ecosystem | Fix (by version range) / Patch | Released | Source |
|---|---|---|---|
| ubuntu | linux-tools-azure (4.15.0.1130.103) @ trusty | 2026-10-21 | ubuntu |
| redhat | kernel-0:4.18.0-305.49.1.el8_4 | 2022-05-31 | redhat |
| redhat | kernel-rt-0:4.18.0-305.49.1.rt7.121.el8_4 | 2022-05-31 | redhat |
| redhat | kernel-rt-0:4.18.0-372.9.1.rt7.166.el8 | 2022-05-10 | redhat |
| redhat | kernel-0:4.18.0-372.9.1.el8 | 2022-05-10 | redhat |
Patches are aggregated from vendor advisories (Red Hat, Microsoft, Cisco, GitHub) and package ecosystems (OSV, GHSA). Multiple rows for the same upstream release have been deduplicated.
Affected Packages
(7 across 6 ecosystems)
Debian:9(2)
| Package | Vulnerable range | Fix by version range | Dependents |
|---|---|---|---|
| linux | 4.9.107-1 ... 4.9.88-1~bpo8+1 (68 versions) |
| — |
| linux-4.19 | 4.19.132-1~deb9u1 ... 4.19.208-1~deb9u1 (10 versions) |
| — |
Debian:10(1)
| Package | Vulnerable range | Fix by version range | Dependents |
|---|---|---|---|
| linux | 4.19.118-1 ... 4.19.98-1~bpo9+1 (36 versions) |
| — |
Debian:11(1)
| Package | Vulnerable range | Fix by version range | Dependents |
|---|---|---|---|
| linux | 5.10.46-4, 5.10.46-5, 5.10.70-1~bpo10+1 |
| — |
Debian:12(1)
| Package | Vulnerable range | Fix by version range | Dependents |
|---|---|---|---|
| linux | — |
| — |
Debian:13(1)
| Package | Vulnerable range | Fix by version range | Dependents |
|---|---|---|---|
| linux | — |
| — |
Debian:14(1)
| Package | Vulnerable range | Fix by version range | Dependents |
|---|---|---|---|
| linux | — |
| — |
Weakness Classification(1)
MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.
Additional Vendor Advisories
(1)
Vendors that published advisories for this CVE beyond the curated set above. Broader coverage but minimal per-row detail — click through for the original advisory.
Data Freshness Timeline
(refreshed 10× in last 7d / 36× in last 30d)
Each row is a time one of our pipelines fetched, updated or re-scored this CVE. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. An arrow marks a change the record states ("CVSS v3 → 9.1"); EPSS and GHSA rows show the values recorded at that time, not what changed (EPSS values are rounded; hover one for the exact figures). Most recent first.
Showing the most recent 95 of 199 refreshes on record for this CVE.
A repeat, a row identical to one the same pipeline wrote less than 10 seconds earlier, is not a separate refresh and is not counted. 5 repeat rows among the latest 100 are merged into the row they repeat. The 104 oldest rows on record are not shown and were not checked, so the counts can still include repeats.
- 2026-10-23 16:28 UTCEPSS rescoreEPSS 6.9% · 94th percentile
- 2026-10-22 16:29 UTCEPSS rescoreEPSS 6.9% · 94th percentile
- 2026-10-21 16:28 UTCEPSS rescoreEPSS 6.9% · 94th percentile
- 2026-10-21 11:02 UTCEG score recompute
- 2026-10-21 11:02 UTCVendor advisory
- 2026-10-21 11:01 UTCGHSA enrichmentGHSA-x37m-35qq-p254 · GitHub severity CRITICAL · GitHub CVSS 7.4
- 2026-10-20 16:28 UTCEPSS rescoreEPSS 6.9% · 94th percentile
- 2026-10-19 16:28 UTCEPSS rescoreEPSS 6.9% · 94th percentile
- 2026-10-18 09:12 UTCEG score recompute
- 2026-10-17 16:28 UTCEPSS rescoreEPSS 6.9% · 94th percentile
- 2026-10-16 16:33 UTCEPSS rescoreEPSS 6.9% · 94th percentile
- 2026-10-15 16:28 UTCEPSS rescoreEPSS 6.9% · 93rd percentile
- 2026-10-14 16:28 UTCEPSS rescoreEPSS 6.9% · 93rd percentile
- 2026-10-13 16:28 UTCEPSS rescoreEPSS 6.9% · 93rd percentile
- 2026-10-12 19:26 UTCEG score recompute
- 2026-10-12 16:29 UTCEPSS rescoreEPSS 6.9% · 93rd percentile
- 2026-10-11 23:51 UTCEG score recompute
- 2026-10-11 13:43 UTCEPSS rescoreEPSS 6.9% · 93rd percentile
- 2026-10-10 19:56 UTCEPSS rescoreEPSS 6.9% · 93rd percentile
- 2026-10-09 21:33 UTCOSV refresh
- 2026-10-09 20:04 UTCEPSS rescoreEPSS 6.9% · 93rd percentile
- 2026-10-08 16:39 UTCEPSS rescoreEPSS 6.9% · 93rd percentile
- 2026-10-07 23:44 UTCEPSS rescoreEPSS 6.9% · 93rd percentile
- 2026-10-06 15:13 UTCEPSS rescoreEPSS 6.9% · 93rd percentile
- 2026-10-05 17:40 UTCEPSS rescoreEPSS 6.9% · 93rd percentile
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- 2026-10-04 23:18 UTCEPSS rescoreEPSS 6.9% · 93rd percentile
- 2026-10-03 14:22 UTCEPSS rescoreEPSS 6.9% · 93rd percentile
- 2026-10-02 16:22 UTCEPSS rescoreEPSS 6.9% · 93rd percentile
- 2026-10-01 19:46 UTCEPSS rescoreEPSS 6.9% · 93rd percentile
- 2026-09-30 15:28 UTCEG score recompute
- 2026-09-30 15:00 UTCEPSS rescoreEPSS 6.9% · 93rd percentile
- 2026-09-28 13:47 UTCEPSS rescoreEPSS 6.9% · 93rd percentile
- 2026-09-27 13:41 UTCEPSS rescoreEPSS 6.9% · 93rd percentile
- 2026-09-26 15:54 UTCEPSS rescoreEPSS 6.9% · 93rd percentile
- 2026-09-26 00:21 UTCEPSS rescoreEPSS 6.9% · 93rd percentile
- 2026-09-24 14:00 UTCEPSS rescoreEPSS 6.9% · 93rd percentile
- 2026-09-23 13:44 UTCEPSS rescoreEPSS 6.9% · 93rd percentile
- 2026-09-22 14:44 UTCEPSS rescoreEPSS 6.8% · 93rd percentile
- 2026-09-21 20:28 UTCEPSS rescoreEPSS 6.8% · 93rd percentile
- 2026-09-20 05:38 UTCOSV refresh
- 2026-09-19 15:37 UTCEPSS rescoreEPSS 6.8% · 93rd percentile
- 2026-09-18 19:23 UTCEPSS rescoreEPSS 6.8% · 93rd percentile
- 2026-09-17 19:23 UTCEPSS rescoreEPSS 6.8% · 93rd percentile
- 2026-09-16 14:04 UTCEPSS rescoreEPSS 6.8% · 93rd percentile
- 2026-09-15 03:06 UTCEPSS rescoreEPSS 6.8% · 93rd percentile
- 2026-09-12 14:57 UTCEPSS rescoreEPSS 6.8% · 93rd percentile
- 2026-09-11 09:33 UTCEPSS rescoreEPSS 6.8% · 93rd percentile
- 2026-09-10 09:29 UTCEPSS rescoreEPSS 6.8% · 93rd percentile
- 2026-09-08 21:56 UTCEPSS rescoreEPSS 6.8% · 93rd percentile
- 2026-09-07 15:58 UTCEPSS rescoreEPSS 6.8% · 93rd percentile
- 2026-09-06 13:44 UTCEPSS rescoreEPSS 6.8% · 93rd percentile
- 2026-09-05 15:25 UTCEPSS rescoreEPSS 6.8% · 93rd percentile
- 2026-09-04 13:57 UTCEPSS rescoreEPSS 6.8% · 93rd percentile
- 2026-09-04 05:03 UTCEPSS rescoreEPSS 6.8% · 93rd percentile
- 2026-09-02 14:08 UTCEPSS rescoreEPSS 6.8% · 93rd percentile
- 2026-09-01 13:50 UTCEPSS rescoreEPSS 6.8% · 93rd percentile
- 2026-09-01 08:59 UTCOSV refresh
- 2026-09-01 03:32 UTCEPSS rescoreEPSS 6.8% · 93rd percentile
- 2026-08-30 19:14 UTCEPSS rescoreEPSS 6.8% · 93rd percentile
- 2026-08-30 01:19 UTCEPSS rescoreEPSS 6.8% · 93rd percentile
- 2026-08-28 21:37 UTCEPSS rescoreEPSS 6.8% · 93rd percentile
- 2026-08-27 14:22 UTCEPSS rescoreEPSS 6.8% · 93rd percentile
- 2026-08-26 14:42 UTCEPSS rescoreEPSS 6.8% · 93rd percentile
- 2026-08-25 13:45 UTCEPSS rescoreEPSS 6.8% · 93rd percentile
- 2026-08-23 00:16 UTCEPSS rescoreEPSS 6.8% · 93rd percentile
- 2026-08-21 23:46 UTCEPSS rescoreEPSS 6.8% · 93rd percentile
- 2026-08-20 22:52 UTCEPSS rescoreEPSS 6.8% · 93rd percentile
- 2026-08-19 17:01 UTCEPSS rescoreEPSS 6.8% · 93rd percentile
- 2026-08-18 13:45 UTCEPSS rescoreEPSS 6.8% · 93rd percentile
- 2026-08-16 14:52 UTCEPSS rescoreEPSS 6.8% · 93rd percentile
- 2026-08-16 02:11 UTCEPSS rescoreEPSS 6.8% · 93rd percentile
- 2026-08-15 08:37 UTCOSV refresh
- 2026-08-15 01:27 UTCEPSS rescoreEPSS 6.8% · 93rd percentile
- 2026-08-13 21:57 UTCEPSS rescoreEPSS 6.8% · 93rd percentile
- 2026-08-12 13:47 UTCEPSS rescoreEPSS 6.8% · 93rd percentile
- 2026-08-11 13:38 UTCEPSS rescoreEPSS 6.8% · 93rd percentile
- 2026-08-08 16:33 UTCEPSS rescoreEPSS 6.8% · 93rd percentile
- 2026-08-07 16:23 UTCEPSS rescoreEPSS 6.8% · 93rd percentile
- 2026-08-06 13:43 UTCEPSS rescoreEPSS 6.8% · 93rd percentile
- 2026-08-05 19:14 UTCEPSS rescoreEPSS 6.8% · 93rd percentile
- 2026-08-04 15:06 UTCEPSS rescoreEPSS 6.8% · 93rd percentile
- 2026-08-04 10:34 UTCEPSS rescoreEPSS 6.8% · 93rd percentile
- 2026-08-03 10:32 UTCEPSS rescoreEPSS 6.8% · 93rd percentile
- 2026-08-02 02:24 UTCEPSS rescoreEPSS 6.8% · 93rd percentile
- 2026-08-01 04:12 UTCEPSS rescoreEPSS 6.8% · 93rd percentile
- 2026-07-30 20:25 UTCEG score recompute
- 2026-07-30 20:25 UTCVendor advisory
- 2026-07-30 20:25 UTCGHSA enrichmentGHSA-x37m-35qq-p254 · GitHub severity CRITICAL · GitHub CVSS 7.4
- 2026-07-30 16:25 UTCEPSS rescoreEPSS 6.8% · 93rd percentile
- 2026-07-30 16:23 UTCVendor advisory
- 2026-07-30 16:23 UTCGHSA enrichmentGHSA-x37m-35qq-p254 · GitHub severity CRITICAL · GitHub CVSS 7.4
- 2026-07-30 16:13 UTCEG score recompute
- 2026-07-30 16:13 UTCVendor advisory
- 2026-07-30 16:13 UTCGHSA enrichmentGHSA-x37m-35qq-p254 · GitHub severity CRITICAL · GitHub CVSS 7.4
- 2026-07-30 01:27 UTCEPSS rescoreEPSS 6.8% · 93rd percentile
Related CVEs(same product + same vendor + same CWE)
Same product
10 shownDebian:9:linux-4.19
Same vendor
10 shownredhat:RHSA-2022:1975 · redhat:RHSA-2022:4829
Frequently asked(5)
What is CVE-2021-20322?
When was the CVE record for CVE-2021-20322 published?
Is CVE-2021-20322 actively exploited?
What is the CVSS score of CVE-2021-20322?
How do I remediate CVE-2021-20322?
Dependency Blast Radius
See which npm, PyPI, Go, and Maven packages are affected by CVE-2021-20322
Is Your Infrastructure Affected by CVE-2021-20322?
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