CVE-2017-9227: An issue was discovered in Oniguruma 6.2.0, as used in Oniguruma-mod in Ruby through 2.4.1 and mbstring in PHP

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CRITICAL 9.8REMOTEDOWNGRADEUPGRADE

CVE-2017-9227 is a critical-severity flaw (CVSS 9.8) affecting oniguruma, php. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

An issue was discovered in Oniguruma 6.2.0, as used in Oniguruma-mod in Ruby through 2.4.1 and mbstring in PHP through 7.1.5. A stack out-of-bounds read occurs in mbc_enc_len() during regular expression searching. Invalid handling of reg->dmin in forward_search_range() could result in an invalid pointer dereference, as an out-of-bounds read from a stack buffer.

Why this priority

Critical severity
EPSS top 6%: very likely to be exploited
Public exploit reference
Remotely exploitable, no login, no user action

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	6.3% (top 6%)
CISA exploited list	No
Weakness	CWE-125
Published	2017-05-24
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: oniguruma project · php

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

Am I affected?

Timeline

2017-05-24 15:29 UTCPublished CVE record published
2026-06-17 01:27 UTCUpdated Record last modified

oniguruma project oniguruma DOWNGRADE

Affected: 6.2.0

Fixed in: no fixed release known

Safe to downgrade to: a release before 6.2.0

1. Check installed version

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

2. No fixed release: DOWNGRADE to a release before 6.2.0 (Debian / Ubuntu)

apt-cache madison oniguruma sudo apt install oniguruma=<VERSION_BEFORE_6.2.0> sudo apt-mark hold oniguruma

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

dnf --showduplicates list oniguruma sudo dnf downgrade oniguruma-<VERSION_BEFORE_6.2.0> sudo dnf versionlock add oniguruma

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.

php php UPGRADE

Affected: >= 5.6.0 and < 5.6.31 · >= 7.0.0 and < 7.0.21 · >= 7.1.0 and < 7.1.7

Fixed in: 5.6.31, 7.0.21, 7.1.7

Safe to downgrade to: a release before 5.6.0

1. Check installed version

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

2. UPGRADE to 5.6.31 (Debian / Ubuntu)

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

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade php

Note

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

3. If no update is available yet, DOWNGRADE to a release before 5.6.0 (Debian / Ubuntu)

apt-cache madison php sudo apt install php=<VERSION_BEFORE_5.6.0> sudo apt-mark hold php

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list php sudo dnf downgrade php-<VERSION_BEFORE_5.6.0> sudo dnf versionlock add php

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-2017-9227?

oniguruma: downgrade or apply the listed mitigation; php: upgrade to 5.6.31, 7.0.21, 7.1.7. Exact commands for each OS are on this page.

Is CVE-2017-9227 being exploited?

CVE-2017-9227 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-2017-9227 affect?

CVE-2017-9227 affects oniguruma, php. Severity is critical (CVSS 9.8). An issue was discovered in Oniguruma 6.2.0, as used in Oniguruma-mod in Ruby through 2.4.1 and mbstring in PHP through 7.1.5. A stack out-of-bounds read occurs in mbc_enc_len() during regular expression searching. Invalid handling of reg->d

How urgent is CVE-2017-9227?

Priority 68/100. Critical severity; EPSS top 6%: very likely to be exploited; Public exploit reference; Remotely exploitable, no login, no user action

Software pages

PHP vulnerabilities · Ruby vulnerabilities

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References

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