How severe is CVE-2017-17821?

CVE-2017-17821 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2017-17821 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (71st percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2017-17821?

CVE-2017-17821 affects Apple Safari. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2017-17821?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.

When was CVE-2017-17821 published?

CVE-2017-17821 was published on 2017-12-21 and last updated on 2026-06-17.

CVE-2017-17821

CVE-2017-17821 is a critical-severity vulnerability in Apple Safari with a CVSS 3.x base score of 9.8. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-119.

Key facts

Severity: Critical (CVSS 3.x base score 9.8)
CVSS v2: 7.5
EPSS exploit prediction: 1% (71st percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-119
Affected product: Apple Safari
Published: 2017-12-21
Last modified: 2026-06-17

Description

WTF/wtf/FastBitVector.h in WebKit, as distributed in Safari Technology Preview Release 46, allows remote attackers to cause a denial of service (buffer overflow) or possibly have unspecified other impact because it calls the FastBitVectorWordOwner::resizeSlow function (in WTF/wtf/FastBitVector.cpp) for a purpose other than initializing a bitvector size, and resizeSlow mishandles cases where the old array length is greater than the new array length.

Frequently asked questions

What is CVE-2017-17821?: WTF/wtf/FastBitVector.h in WebKit, as distributed in Safari Technology Preview Release 46, allows remote attackers to cause a denial of service (buffer overflow) or possibly have unspecified other impact because it calls the FastBitVectorWordOwner::resizeSlow function (in WTF/wtf/FastBitVector.cpp) for a purpose other than initializing a bitvector size, and resizeSlow mishandles cases where the old array length is greater than the new array length.
How severe is CVE-2017-17821?: CVE-2017-17821 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2017-17821 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (71st percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2017-17821?: CVE-2017-17821 affects Apple Safari. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2017-17821?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.
When was CVE-2017-17821 published?: CVE-2017-17821 was published on 2017-12-21 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:apple:safari:46:*:*:*:technology_preview:*:*:*

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