CVE-2012-1823: PHP-CGI Query String Parameter Vulnerability

Q: How do I fix CVE-2012-1823?

php: upgrade to 5.3.12, 5.4.2; fedora: mitigate or apply the listed mitigation; debian linux: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Q: Is CVE-2012-1823 being exploited?

Yes. CVE-2012-1823 is on the CISA Known Exploited Vulnerabilities list, so treat it as patch-now.

Q: What does CVE-2012-1823 affect?

CVE-2012-1823 affects php, fedora, debian linux. Severity is critical (CVSS 9.8). sapi/cgi/cgi_main.c in PHP before 5.3.12 and 5.4.x before 5.4.2, when configured as a CGI script (aka php-cgi), does not properly handle query strings that lack an = (equals sign) character, which allows remote attackers to execute arbitrar

Q: How urgent is CVE-2012-1823?

Priority 100/100. Critical severity; EPSS top 1%: very likely to be exploited; Exploited in the wild (CISA KEV); Public exploit reference; CISA SSVC: automatable with total technical impact; Remotely exploitable, no login, no user action; On your watchlist

100

Patch now

CRITICAL 9.8EXPLOITEDREMOTEWATCHLISTUPGRADEMITIGATEMITIGATE

CVE-2012-1823 is a critical-severity flaw (CVSS 9.8) affecting php, fedora, debian linux, reported as exploited in the wild. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

sapi/cgi/cgi_main.c in PHP before 5.3.12 and 5.4.x before 5.4.2, when configured as a CGI script (aka php-cgi), does not properly handle query strings that lack an = (equals sign) character, which allows remote attackers to execute arbitrary code by placing command-line options in the query string, related to lack of skipping a certain php_getopt for the 'd' case.

Why this priority

Critical severity
EPSS top 1%: very likely to be exploited
Exploited in the wild (CISA KEV)
Public exploit reference
CISA SSVC: automatable with total technical impact
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	100.0% (top 1%)
CISA exploited list	Yes, fix due 2022-04-15
Weakness	CWE-77
Published	2012-05-11
Last modified	2026-06-16

Publisher (CNA): CERT/CC · Vendor: debian · fedoraproject · hp · opensuse · php · suse

Last updated 2026-06-16 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2012-05-11 10:15 UTCPublished CVE record published
2022-03-25Exploited Added to the CISA Known Exploited Vulnerabilities list
2022-04-15Deadline CISA due date for US federal agencies to patch
2026-06-16 23:40 UTCUpdated Record last modified

php php UPGRADE

Affected: < 5.3.12 · >= 5.4.0 and < 5.4.2

Fixed in: 5.3.12, 5.4.2

Safe to downgrade to: a release before 5.4.0

1. Check installed version

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

2. UPGRADE to 5.3.12 (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 5.4.0 (Debian / Ubuntu)

apt-cache madison php sudo apt install php=<VERSION_BEFORE_5.4.0> 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_5.4.0> 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.

fedoraproject fedora MITIGATE

Affected: 39 · 40

Fixed in: no fixed release known

Safe to downgrade to: a release before 39

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.

debian debian linux MITIGATE

Affected: 6.0

Fixed in: no fixed release known

Safe to downgrade to: a release before 6.0

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.

hp hp-ux MITIGATE

Affected: b.11.23 · b.11.31

Fixed in: no fixed release known

Safe to downgrade to: a release before b.11.23

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.

opensuse opensuse MITIGATE

Affected: 11.4 · 12.1

Fixed in: no fixed release known

Safe to downgrade to: a release before 11.4

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.

suse linux enterprise server MITIGATE

Affected: 10 sp4

Fixed in: no fixed release known

Safe to downgrade to: a release before 10

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.

Exact fixes by distribution

A distro patch exists: prefer upgrading over downgrading.

Fedora 46 · dupeguru · FIXED · 4.3.1^20261101git7a2c79f-1.fc46 · FEDORA-2026-fe4523382c · source

sudo dnf upgrade --advisory=FEDORA-2026-fe4523382c

Fedora ELN · openexr · FIXED · 3.4.13-3.eln159 · FEDORA-2026-827a613db5 · source

sudo dnf upgrade --advisory=FEDORA-2026-827a613db5

RHEL 5 · php · FIXED · php-5.1.6-34.el5_8

sudo dnf upgrade --advisory=RHSA-2012:0546 rpm -q php

RHEL 5 · php53 · FIXED · php53-5.3.3-7.el5_8

sudo dnf upgrade --advisory=RHSA-2012:0547 rpm -q php53

RHEL 5.3 Long Life · php · FIXED · php-5.1.6-23.3.el5_3

sudo dnf upgrade --advisory=RHSA-2012:0568 rpm -q php

RHEL 5.6 EUS - Server Only · php · FIXED · php-5.1.6-27.el5_6.4

sudo dnf upgrade --advisory=RHSA-2012:0568 rpm -q php

RHEL 5.6 EUS - Server Only · php53 · FIXED · php53-5.3.3-1.el5_6.2

sudo dnf upgrade --advisory=RHSA-2012:0569 rpm -q php53

Amazon Linux 1 · see advisory · FIXED · ALAS-2012-77 · source

sudo yum update --advisory=ALAS-2012-77

Public exploits and detection

Public code exists for this CVE. Treat unpatched systems as at risk, and only run PoCs in a lab.

GitHub PoC: 0xl0k1/CVE-2012-1823 (12 stars)
GitHub PoC: Unix13/metasploitable2 (4 stars)
Exploit-DB: Apache + PHP < 5.3.12 / < 5.4.2 - cgi-bin Remote Code Execution
Exploit-DB: Apache + PHP < 5.3.12 / < 5.4.2 - Remote Code Execution + Scanner
Exploit-DB: PHP 5.3.12/5.4.2 - CGI Argument Injection (Metasploit)
Exploit-DB: PHP < 5.3.12 / < 5.4.2 - CGI Argument Injection
Metasploit: PHP CGI Argument Injection
Nuclei scan template: PHP CGI v5.3.12/5.4.2 Remote Code Execution

Advisories and coverage

Research and news

Tenable Research: php2shell (CVE-2026-109618, CVE-2026-109619): Frequently asked questions about critical PHP remote code execution vulnerabilities 2026-10-21

Verify at the official source NVD · CVE Program · CISA KEV catalog · 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-2012-1823?

php: upgrade to 5.3.12, 5.4.2; fedora: mitigate or apply the listed mitigation; debian linux: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2012-1823 being exploited?

Yes. CVE-2012-1823 is on the CISA Known Exploited Vulnerabilities list, so treat it as patch-now.

What does CVE-2012-1823 affect?

CVE-2012-1823 affects php, fedora, debian linux. Severity is critical (CVSS 9.8). sapi/cgi/cgi_main.c in PHP before 5.3.12 and 5.4.x before 5.4.2, when configured as a CGI script (aka php-cgi), does not properly handle query strings that lack an = (equals sign) character, which allows remote attackers to execute arbitrar

How urgent is CVE-2012-1823?

Priority 100/100. Critical severity; EPSS top 1%: very likely to be exploited; Exploited in the wild (CISA KEV); Public exploit reference; CISA SSVC: automatable with total technical impact; Remotely exploitable, no login, no user action; On your watchlist

Software pages

PHP vulnerabilities · Debian vulnerabilities

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References

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