CVE-2025-23419: When multiple server blocks are configured to share the same IP address and port, an attacker can use session

This month

MEDIUM 4.3WATCHLISTUPGRADEUPGRADEMITIGATE

CVE-2025-23419 is a medium-severity flaw (CVSS 4.3) affecting nginx, nginx plus, debian linux. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

When multiple server blocks are configured to share the same IP address and port, an attacker can use session resumption to bypass client certificate authentication requirements on these servers. This vulnerability arises when TLS Session Tickets https://nginx.org/en/docs/http/ngx_http_ssl_module.html#ssl_session_ticket_key are used and/or the SSL session cache https://nginx.org/en/docs/http/ngx_http_ssl_module.html#ssl_session_cache are used

Why this priority

On your watchlist

A fixed release or distro patch exists.

Risk facts

CVSS score	4.3 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	Low
User interaction	None
EPSS exploit chance	2.8% (top 14%)
CISA exploited list	No
Weakness	CWE-863
Published	2025-02-05
Last modified	2026-06-17

Publisher (CNA): F5 Networks · Vendor: debian · f5

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

Am I affected?

Timeline

2025-02-05 18:15 UTCPublished CVE record published
2026-06-17 08:54 UTCUpdated Record last modified

f5 nginx UPGRADE

Affected: >= 1.11.4 and < 1.26.3 · >= 1.27.0 and < 1.27.4

Fixed in: 1.26.3, 1.27.4

Safe to downgrade to: a release before 1.11.4

1. Check installed version

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

2. UPGRADE to 1.26.3 (Debian / Ubuntu)

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

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade nginx

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 1.11.4 (Debian / Ubuntu)

apt-cache madison nginx sudo apt install nginx=<VERSION_BEFORE_1.11.4> sudo apt-mark hold nginx

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

dnf --showduplicates list nginx sudo dnf downgrade nginx-<VERSION_BEFORE_1.11.4> sudo dnf versionlock add nginx

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.

f5 nginx plus UPGRADE

Affected: >= r28 and < r32 · r32 · r32 p1 · r33 · r33 p1

Fixed in: r32

Safe to downgrade to: a release before r28

1. Check installed version

apt-cache policy nginx-plus || rpm -q nginx-plus || nginx-plus --version

2. UPGRADE to r32 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade nginx-plus

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade nginx-plus

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 r28 (Debian / Ubuntu)

apt-cache madison nginx-plus sudo apt install nginx-plus=<VERSION_BEFORE_r28> sudo apt-mark hold nginx-plus

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

dnf --showduplicates list nginx-plus sudo dnf downgrade nginx-plus-<VERSION_BEFORE_r28> sudo dnf versionlock add nginx-plus

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.

debian debian linux MITIGATE

Affected: 11.0

Fixed in: no fixed release known

Safe to downgrade to: a release before 11.0

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.

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-2025-23419?

nginx: upgrade to 1.26.3, 1.27.4; nginx plus: upgrade to r32; debian linux: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2025-23419 being exploited?

CVE-2025-23419 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-2025-23419 affect?

CVE-2025-23419 affects nginx, nginx plus, debian linux. Severity is medium (CVSS 4.3). When multiple server blocks are configured to share the same IP address and port, an attacker can use session resumption to bypass client certificate authentication requirements on these servers. This vulnerability arises when TLS Session

How urgent is CVE-2025-23419?

Priority 42/100. On your watchlist

Software pages

nginx vulnerabilities · Debian vulnerabilities · F5 BIG-IP vulnerabilities

References

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