CVE-2016-6354: Heap-based buffer overflow in the yy_get_next_buffer function in Flex before 2.6.1 might allow context-depende

Q: How do I fix CVE-2016-6354?

debian linux: mitigate or apply the listed mitigation; flex: upgrade to newer than 2.6.0. Exact commands for each OS are on this page.

Q: Is CVE-2016-6354 being exploited?

CVE-2016-6354 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2016-6354 affect?

CVE-2016-6354 affects debian linux, flex. Severity is critical (CVSS 9.8). Heap-based buffer overflow in the yy_get_next_buffer function in Flex before 2.6.1 might allow context-dependent attackers to cause a denial of service or possibly execute arbitrary code via vectors involving num_to_read.

Q: How urgent is CVE-2016-6354?

Priority 68/100. Critical severity; EPSS top 5%: very likely to be exploited; Remotely exploitable, no login, no user action; On your watchlist

This week

CRITICAL 9.8REMOTEWATCHLISTMITIGATEUPGRADE

CVE-2016-6354 is a critical-severity flaw (CVSS 9.8) affecting debian linux, flex. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Heap-based buffer overflow in the yy_get_next_buffer function in Flex before 2.6.1 might allow context-dependent attackers to cause a denial of service or possibly execute arbitrary code via vectors involving num_to_read.

Why this priority

Critical severity
EPSS top 5%: very likely to be exploited
Remotely exploitable, no login, no user action
On your watchlist

A fixed release or distro patch exists.

Risk facts

CVSS score	9.8 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	9.1% (top 5%)
CISA exploited list	No
Weakness	CWE-119
Published	2016-09-21
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: debian · westes

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

Am I affected?

Timeline

2016-09-21 14:25 UTCPublished CVE record published
2026-06-17 00:50 UTCUpdated Record last modified

debian debian linux MITIGATE

Affected: 8.0

Fixed in: no fixed release known

Safe to downgrade to: a release before 8.0

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

westes flex UPGRADE

Affected: <= 2.6.0

Fixed in: newer than 2.6.0

Safe to downgrade to: no unaffected older release

1. Check installed version

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

2. UPGRADE to newer than 2.6.0 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade flex

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade flex

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

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-2016-6354?

debian linux: mitigate or apply the listed mitigation; flex: upgrade to newer than 2.6.0. Exact commands for each OS are on this page.

Is CVE-2016-6354 being exploited?

CVE-2016-6354 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-2016-6354 affect?

CVE-2016-6354 affects debian linux, flex. Severity is critical (CVSS 9.8). Heap-based buffer overflow in the yy_get_next_buffer function in Flex before 2.6.1 might allow context-dependent attackers to cause a denial of service or possibly execute arbitrary code via vectors involving num_to_read.

How urgent is CVE-2016-6354?

Priority 68/100. Critical severity; EPSS top 5%: very likely to be exploited; Remotely exploitable, no login, no user action; On your watchlist

Software pages

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References

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