VulnerabilityPublished 7 Oct 2026Updated 27 Oct 2026

CVE-2026-77214: libexpat · Out-of-bounds Read

Affects libexpatSource CVE Database V5

Not known to be exploited · CVSS 8.3 High.

Data as of 27 Oct 2026, 10:42 UTC

CVSS 4.0 base score

8.3High

How severe the flaw is on the 0–10 CVSS scale.

Exploitation: No evidence of active exploitation and no public proof of concept
Automatable: Attackers can reliably automate steps 1–4 of the kill chain
Technical impact: Limited control over the software or limited information exposure

CISA SSVC assessment, 2026-10-10.

CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:N/VA:L/SC:N/SI:N/SA:N

Attack Vector: Network
Attack Complexity: Low
Attack Requirements: Present
Privileges Required: None
User Interaction: None
Vulnerable system confidentiality: High
Vulnerable system integrity: None
Vulnerable system availability: Low
Subsequent system confidentiality: None
Subsequent system integrity: None
Subsequent system availability: None

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable system is bound to the network stack and the set of possible attackers extends beyond the other options listed below, up to and including the entire Internet. Such a vulnerability is often termed “remotely exploitable” and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: The attacker must take no measurable action to exploit the vulnerability. The attack requires no target-specific circumvention to exploit the vulnerability. An attacker can expect repeatable success against the vulnerable system.
Attack Requirements: Present: The successful attack depends on the presence of specific deployment and execution conditions of the vulnerable system that enable the attack. These include: a race condition must be won to successfully exploit the vulnerability (the successfulness of the attack is conditioned on execution conditions that are not under full control of the attacker, or the attack may need to be launched multiple times against a single target before being successful); the attacker must inject themselves into the logical network path between the target and the resource requested by the victim (e.g. vulnerabilities requiring an on-path attacker).
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files of the vulnerable system to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without interaction from any human user, other than the attacker.
Vulnerable system confidentiality: High: There is a total loss of confidentiality, resulting in all information within the Vulnerable System being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact. For example, an attacker steals the administrator's password, or private encryption keys of a web server.
Vulnerable system integrity: None: There is no loss of integrity within the Vulnerable System.
Vulnerable system availability: Low: Performance is reduced or there are interruptions in resource availability. Even if repeated exploitation of the vulnerability is possible, the attacker does not have the ability to completely deny service to legitimate users. The resources in the Vulnerable System are either partially available all of the time, or fully available only some of the time, but overall there is no direct, serious consequence to the Vulnerable System.
Subsequent system confidentiality: None: There is no loss of confidentiality within the Subsequent System or all confidentiality impact is constrained to the Vulnerable System.
Subsequent system integrity: None: There is no loss of integrity within the Subsequent System or all integrity impact is constrained to the Vulnerable System.
Subsequent system availability: None: There is no impact to availability within the Subsequent System or all availability impact is constrained to the Vulnerable System.

Definitions: FIRST CVSS v4.0 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 7 Oct 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Affected software

Product	Affected	Fixed in
libexpatlibexpat	Affected <=2.8.5	Fixed in–
GitHublibexpat`pkg:github/libexpat`Other threats	Affected <=2.8.5	Fixed in–

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

Until a fix is available, users should consider avoiding use of affected libexpat versions or apply any vendor-provided mitigations once announced.

Description

CVE-2026-77214 is a heap buffer over-read vulnerability in libexpat versions up to 2.8.5. The flaw occurs in xmlparse.c where XML_ParseBuffer advances the parse buffer end using a caller-supplied length without validating it against the allocated buffer size. This can cause out-of-bounds reads of heap memory during XML parsing, potentially disclosing sensitive pointers that could aid in bypassing ASLR and enable further exploitation.

Impact

Successful exploitation of this vulnerability allows an attacker to read out-of-bounds heap memory, potentially disclosing sensitive information such as heap pointers and code pointers. This information disclosure can facilitate bypassing Address Space Layout Randomization (ASLR), increasing the likelihood of successful exploitation of other vulnerabilities. The CVSS 4.0 score of 8.3 indicates a high severity with network attack vector, low attack complexity, no privileges or user interaction required, and high impact on confidentiality.

Summary

The vulnerability in libexpat before commit 13c5f63 involves an out-of-bounds read in xmlparse.c due to improper validation of the length parameter in XML_ParseBuffer. The function increments parser->m_bufferEnd by a caller-supplied length without checking if it exceeds the allocated buffer size. When multiple XML_ParseBuffer calls occur, m_bufferEnd can move beyond the heap allocation, causing subsequent parsing to read adjacent heap memory. This memory disclosure can reveal heap pointers, libc function pointers, and code pointers, which attackers can use to defeat ASLR and develop additional exploitation techniques. The vulnerability requires a parse buffer to be present, typically allocated by prior XML_GetBuffer or XML_Parse calls. The affected versions are libexpat versions up to and including 2.8.5.

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 27 Oct 2026, 10:29 UTC

Technical details

References

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