CVE-2016-9643: The regex code in Webkit 2.4.11 allows remote attackers to cause a denial of service (memory consumption) as d

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HIGH 7.5REMOTEDOWNGRADE

CVE-2016-9643 is a high-severity flaw (CVSS 7.5) affecting webkit. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

The regex code in Webkit 2.4.11 allows remote attackers to cause a denial of service (memory consumption) as demonstrated in a large number of ($ (open parenthesis and dollar) followed by {-2,16} and a large number of +) (plus close parenthesis).

Why this priority

High severity
Remotely exploitable, no login, no user action

No fix is published yet: follow the downgrade or mitigation steps.

Risk facts

CVSS score	7.5 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	3.1% (top 12%)
CISA exploited list	No
Weakness	CWE-400
Published	2017-03-07
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: webkit

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2017-03-07 16:59 UTCPublished CVE record published
2026-06-17 00:56 UTCUpdated Record last modified

webkit webkit DOWNGRADE

Affected: 2.4.11

Fixed in: no fixed release known

Safe to downgrade to: a release before 2.4.11

1. Check installed version

apt-cache policy webkit || rpm -q webkit || webkit --version

2. No fixed release: DOWNGRADE to a release before 2.4.11 (Debian / Ubuntu)

apt-cache madison webkit sudo apt install webkit=<VERSION_BEFORE_2.4.11> sudo apt-mark hold webkit

2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list webkit sudo dnf downgrade webkit-<VERSION_BEFORE_2.4.11> sudo dnf versionlock add webkit

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2016-9643?

webkit: downgrade or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2016-9643 being exploited?

CVE-2016-9643 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2016-9643 affect?

CVE-2016-9643 affects webkit. Severity is high (CVSS 7.5). The regex code in Webkit 2.4.11 allows remote attackers to cause a denial of service (memory consumption) as demonstrated in a large number of ($ (open parenthesis and dollar) followed by {-2,16} and a large number of +) (plus close parenth

How urgent is CVE-2016-9643?

Priority 53/100. High severity; Remotely exploitable, no login, no user action

Software pages

WebKit vulnerabilities · Apple Safari and WebKit vulnerabilities

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References

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