CVE-2026-40542: Missing critical step in authentication in Apache HttpClient 5.6 allows an attacker to cause the client to acc

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HIGH 7.3REMOTEWATCHLISTDOWNGRADE

CVE-2026-40542 is a high-severity flaw (CVSS 7.3) affecting httpclient. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Missing critical step in authentication in Apache HttpClient 5.6 allows an attacker to cause the client to accept SCRAM-SHA-256 authentication without proper mutual authentication verification. Users are recommended to upgrade to version 5.6.1, which fixes this issue.

Why this priority

High severity
Remotely exploitable, no login, no user action
On your watchlist

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

Risk facts

CVSS score	7.3 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.5% (top 55%)
CISA exploited list	No
Weakness	CWE-304, CWE-325
Published	2026-04-22
Last modified	2026-10-26

Publisher (CNA): Apache Software Foundation · Vendor: apache

Last updated 2026-10-26 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-04-22 08:16 UTCPublished CVE record published
2026-10-26 21:10 UTCUpdated Record last modified

apache httpclient DOWNGRADE

Affected: 5.6

Fixed in: no fixed release known

Safe to downgrade to: a release before 5.6

1. Check installed version

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

2. No fixed release: DOWNGRADE to a release before 5.6 (Debian / Ubuntu)

apt-cache madison httpclient sudo apt install httpclient=<VERSION_BEFORE_5.6> sudo apt-mark hold httpclient

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

dnf --showduplicates list httpclient sudo dnf downgrade httpclient-<VERSION_BEFORE_5.6> sudo dnf versionlock add httpclient

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-2026-40542?

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

Is CVE-2026-40542 being exploited?

CVE-2026-40542 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-2026-40542 affect?

CVE-2026-40542 affects httpclient. Severity is high (CVSS 7.3). Missing critical step in authentication in Apache HttpClient 5.6 allows an attacker to cause the client to accept SCRAM-SHA-256 authentication without proper mutual authentication verification. Users are recommended to upgrade to version 5.

How urgent is CVE-2026-40542?

Priority 47/100. High severity; Remotely exploitable, no login, no user action; On your watchlist

Related CVEs

CVE-2026-71290 CRITICAL 9.1 UPGRADE Improper TLS hostname verification vulnerability in Apache HttpComponents Client 5.4 or newer. HostnameVerific
CVE-2026-64607 MEDIUM 5.3 UPGRADE HttpClient based on the classic i/o model fails to correctly release the underlying connection back to the con

References

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