CVE-2026-34479 | Apache Log4j 1 to Log4j 2 bridge: Silent log event loss in Log4j1XmlLayout due to unescaped XML 1.0 forbidden characters

Exp

The Log4j1XmlLayout from the Apache Log4j 1-to-Log4j 2 bridge fails to escape characters forbidden by the XML 1.0 standard, producing malformed XML output. Conforming XML parsers are required to reject documents containing such characters with a fatal error, which may cause downstream log processing systems to drop or fail to index affected records. Two groups of users are affected: * Those using Log4j1XmlLayout directly in a Log4j Core 2 configuration file. * Those using the Log4j 1 configuration compatibility layer with org.apache.log4j.xml.XMLLayout specified as the layout class. Users are advised to upgrade to Apache Log4j 1-to-Log4j 2 bridge version 2.25.4, which corrects this issue. Note: The Apache Log4j 1-to-Log4j 2 bridge is deprecated and will not be present in Log4j 3. Users are encouraged to consult the Log4j 1 to Log4j 2 migration guide https://logging.apache.org/log4j/2.x/migrate-from-log4j1.html , and specifically the section on eliminating reliance on the bridge.

Published: 2026-04-10 Last update: 2026-05-06 Assigner: [email protected] Source: [email protected]
NVD Status：Analyzed，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2026-34479 is rated Exploit Available (53.5/100): CVSS Medium severity, with low exploitation likelihood (EPSS 0.13%). 1 public exploit reference(s) are indexed (Exploit-DB). Public exploits are available—assess exposure, apply mitigations, and prioritize patching.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Public exploit references (Exploit-DB) for CVE-2026-34479

EDB-ID Source Kind Published Link
— nvd_ref exploit_tag Exploit-DB ↗

Exploit prediction scoring system (EPSS) score for CVE-2026-34479

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-05-22 0.16% 0.13% -0.03%
2 2026-04-16 0.12% 0.16% +0.04%
3 2026-04-11 — 0.12% —

Full EPSS history (3 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2026-34479

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
6.9 4.0 MEDIUM
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:N/SI:L/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network.
Attack complexity (AC:L)
Exploitation conditions are straightforward and stable.
Attack requirements (AT:N)
No additional preconditions are required beyond normal reachability.
Privileges required (PR:N)
No privileges are required.
User interaction (UI:N)
No user interaction is required.
Vulnerable system confidentiality impact (VC:N)
No confidentiality impact on the vulnerable system.
Vulnerable system integrity impact (VI:N)
No integrity impact on the vulnerable system.
Vulnerable system availability impact (VA:N)
No availability impact on the vulnerable system.
Subsequent system confidentiality impact (SC:N)
No confidentiality impact on subsequent systems.
Subsequent system integrity impact (SI:L)
Limited integrity impact on subsequent systems.
Subsequent system availability impact (SA:N)
No availability impact on subsequent systems.
Exploit maturity (threat) (E:X)
Not defined: no reliable threat intelligence; scoring assumes the worst case (equivalent to Attacked).
Confidentiality requirement (CR:X)
Not defined: insufficient information; scoring treats this like High (worst case).
Integrity requirement (IR:X)
Not defined: insufficient information; scoring treats this like High (worst case).
Availability requirement (AR:X)
Not defined: insufficient information; scoring treats this like High (worst case).
Modified attack vector (MAV:X)
Not defined: scoring uses the Base Attack Vector (AV).
Modified attack complexity (MAC:X)
Not defined: scoring uses the Base Attack Complexity (AC).
Modified attack requirements (MAT:X)
Not defined: scoring uses the Base Attack Requirements (AT).
Modified privileges required (MPR:X)
Not defined: scoring uses the Base Privileges Required (PR).
Modified user interaction (MUI:X)
Not defined: scoring uses the Base User Interaction (UI).
Modified vulnerable system confidentiality impact (MVC:X)
Not defined: scoring uses the Base VC metric.
Modified vulnerable system integrity impact (MVI:X)
Not defined: scoring uses the Base VI metric.
Modified vulnerable system availability impact (MVA:X)
Not defined: scoring uses the Base VA metric.
Modified subsequent system confidentiality impact (MSC:X)
Not defined: scoring uses the Base SC metric.
Modified subsequent system integrity impact (MSI:X)
Not defined: scoring uses the Base SI metric.
Modified subsequent system availability impact (MSA:X)
Not defined: scoring uses the Base SA metric.
Safety (supplemental) (S:X)
Not evaluated.
Automatable (supplemental) (AU:X)
Not evaluated.
Recovery (supplemental) (R:X)
Not evaluated.
Value density (supplemental) (V:X)
Not evaluated.
Vulnerability response effort (supplemental) (RE:X)
Not evaluated.
Provider urgency (supplemental) (U:X)
Not evaluated.
 — — [email protected]
7.5 3.1 HIGH
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:N)
Service keeps running; no real outage angle.
 3.9 3.6 [email protected]

Weakness enumeration for CVE-2026-34479

GitHub Security Advisory for CVE-2026-34479

GHSA-h383-gmxw-35v2 · Severity: medium · Ecosystem: maven — Apache Log4j 1 to Log4j 2 bridge: silent log event loss in Log4j1XmlLayout due to unescaped XML 1.0 forbidden characters

OS Trackers for CVE-2026-34479

vendor priority summary link
debian unimportant CVE-2026-34479 unimportant priority: Debian including 2 source packages (apache-log4j1.2, apache-log4j2), 10 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): open 5, resolved 5. https://security-tracker.debian.org/tracker/CVE-2026-34479
redhat medium — https://access.redhat.com/security/cve/CVE-2026-34479
suse medium CVE-2026-34479 severity moderate: SUSE including 15 source package names (log4j, log4j-2.20.0-150200.4.33.1, …), 23 product×package rows across 8 product lines (SUSE Linux Enterprise Module for Basesystem 15 SP7, SUSE Linux Enterprise Server 12 SP4-LTSS, … (8 product lines)): Fixed 9, First Fixed 8, Known Not Affected 6. https://www.suse.com/security/cve/CVE-2026-34479/
ubuntu medium CVE-2026-34479 medium priority: Ubuntu including 2 source packages (apache-log4j1.2, apache-log4j2), 15 status rows across 8 suites (bionic, focal, jammy, noble, questing, trusty, upstream, xenial): needs-triage 14, not-affected 1. https://ubuntu.com/security/CVE-2026-34479

Affected software / configurations for CVE-2026-34479

Vendor Product Version Raw CPE
apache log4j >= 2.7, < 2.25.4 cpe:2.3:a:apache:log4j:*:*:*:*:*:*:*:*
apache log4j 3.0.0 cpe:2.3:a:apache:log4j:3.0.0:alpha1:*:*:*:*:*:*
apache log4j 3.0.0 cpe:2.3:a:apache:log4j:3.0.0:alpha1_rc1:*:*:*:*:*:*
apache log4j 3.0.0 cpe:2.3:a:apache:log4j:3.0.0:alpha1_rc2:*:*:*:*:*:*
apache log4j 3.0.0 cpe:2.3:a:apache:log4j:3.0.0:beta1:*:*:*:*:*:*
apache log4j 3.0.0 cpe:2.3:a:apache:log4j:3.0.0:beta2:*:*:*:*:*:*

References for CVE-2026-34479

cvelogic Threat Intelligence