CVE-2020-26154: url.cpp in libproxy through 0.4.15 is prone to a buffer overflow when PAC is enabled, as demonstrated by a lar

Q: How do I fix CVE-2020-26154?

libproxy: upgrade to newer than 0.4.15; 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-2020-26154 being exploited?

CVE-2020-26154 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-2020-26154 affect?

CVE-2020-26154 affects libproxy, fedora, debian linux. Severity is critical (CVSS 9.8). url.cpp in libproxy through 0.4.15 is prone to a buffer overflow when PAC is enabled, as demonstrated by a large PAC file that is delivered without a Content-length header.

Q: How urgent is CVE-2020-26154?

Priority 67/100. Critical severity; Remotely exploitable, no login, no user action; On your watchlist

This week

CRITICAL 9.8REMOTEWATCHLISTUPGRADEMITIGATEMITIGATE

CVE-2020-26154 is a critical-severity flaw (CVSS 9.8) affecting libproxy, fedora, debian linux. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

url.cpp in libproxy through 0.4.15 is prone to a buffer overflow when PAC is enabled, as demonstrated by a large PAC file that is delivered without a Content-length header.

Why this priority

Critical severity
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	3.6% (top 11%)
CISA exploited list	No
Weakness	CWE-120
Published	2020-09-30
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: debian · fedoraproject · libproxy project · opensuse

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

Am I affected?

Timeline

2020-09-30 18:15 UTCPublished CVE record published
2026-06-17 03:07 UTCUpdated Record last modified

libproxy project libproxy UPGRADE

Affected: <= 0.4.15

Fixed in: newer than 0.4.15

Safe to downgrade to: no unaffected older release

1. Check installed version

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

2. UPGRADE to newer than 0.4.15 (Debian / Ubuntu)

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

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade libproxy

Note

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

fedoraproject fedora MITIGATE

Affected: 32 · 33

Fixed in: no fixed release known

Safe to downgrade to: a release before 32

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: 9.0 · 10.0

Fixed in: no fixed release known

Safe to downgrade to: a release before 9.0

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.

opensuse leap MITIGATE

Affected: 15.1 · 15.2

Fixed in: no fixed release known

Safe to downgrade to: a release before 15.1

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.

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-2020-26154?

libproxy: upgrade to newer than 0.4.15; 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-2020-26154 being exploited?

CVE-2020-26154 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-2020-26154 affect?

CVE-2020-26154 affects libproxy, fedora, debian linux. Severity is critical (CVSS 9.8). url.cpp in libproxy through 0.4.15 is prone to a buffer overflow when PAC is enabled, as demonstrated by a large PAC file that is delivered without a Content-length header.

How urgent is CVE-2020-26154?

Priority 67/100. Critical severity; Remotely exploitable, no login, no user action; On your watchlist

Software pages

Debian vulnerabilities

Related CVEs

CVE-2020-25219 HIGH 7.5 UPGRADE MITIGATE url::recvline in url.cpp in libproxy 0.4.x through 0.4.15 allows a remote HTTP server to trigger uncontrolled

References

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