CVE-2025-29786VulnerabilityPublished 17 Mar 2025Updated 23 Jan 2026

CVE-2025-29786: expr · Unthrottled Resource Allocation

Affects exprSource CVE Database V5

Not known to be exploited · CVSS 7.5 High : upgrade to 1.17.0 soon.

Data as of 26 Oct 2026, 06:26 UTC

CVSS 3.1 base score

7.5High

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

EPSS: 0.6% chance of exploitation in 30 days – higher than 49% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 1.17.0

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: None
Availability: High

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

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, 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: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: None: There is no loss of confidentiality within the impacted component.
Integrity: None: There is no loss of integrity within the impacted component.
Availability: High: There is total loss of availability, resulting in the attacker being able to fully deny access to resources in the impacted component; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the impacted component (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable).

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 17 Mar 2025
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 2026-10-26.

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 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

Upgrade github.com/expr-lang/expr to 1.17.0.

Affected software

Product	Affected	Fixed in
Gogithub.com/expr-lang/expr`pkg:golang/github.com/expr-lang/expr`Other threats	Affected <1.17.0	Fixed in 1.17.0

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

AI-suggested

1. Upgrade all instances of the expr-lang library to version 1.17.0 or later, which includes built-in compile-time limits on AST nodes and memory usage to prevent resource exhaustion. 2. For environments where immediate upgrading is not feasible, implement strict input validation to limit the size and complexity of expressions accepted by the parser. This includes setting maximum allowable character lengths and rejecting or truncating inputs exceeding these thresholds. 3. Employ runtime monitoring and alerting on memory usage patterns in services utilizing expr to detect abnormal spikes indicative of attempted exploitation. 4. Use application-layer firewalls or API gateways to enforce input size restrictions and block suspiciously large or malformed expression payloads. 5. Conduct code reviews and penetration testing focused on expression evaluation components to identify and remediate any unbounded input handling. 6. Document and communicate the vulnerability and mitigation steps to development and operations teams to ensure consistent application of safeguards. 7. Consider implementing circuit breakers or resource quotas in container orchestration platforms to limit the impact of potential OOM conditions. These steps collectively reduce the risk of denial-of-service attacks exploiting this vulnerability.

Description

Expr is an expression language and expression evaluation for Go. Prior to version 1.17.0, if the Expr expression parser is given an unbounded input string, it will attempt to compile the entire string and generate an Abstract Syntax Tree (AST) node for each part of the expression. In scenarios where input size isn’t limited, a malicious or inadvertent extremely large expression can consume excessive memory as the parser builds a huge AST. This can ultimately lead to*excessive memory usage and an Out-Of-Memory (OOM) crash of the process. This issue is relatively uncommon and will only manifest when there are no restrictions on the input size, i.e.the expression length is allowed to grow arbitrarily large. In typical use cases where inputs are bounded or validated, this problem would not occur. The problem has been patched in the latest versions of the Expr library. The fix introduces compile-time limits on the number of AST nodes and memory usage during parsing, preventing any single expression from exhausting resources. Users should upgrade to Expr version 1.17.0 or later, as this release includes the new node budget and memory limit safeguards. Upgrading to v1.17.0 ensures that extremely deep or large expressions are detected and safely aborted during compilation, avoiding the OOM condition. For users who cannot immediately upgrade, the recommended workaround is to impose an input size restriction before parsing. In practice, this means validating or limiting the length of expression strings that your application will accept. For example, set a maximum allowable number of characters (or nodes) for any expression and reject or truncate inputs that exceed this limit. By ensuring no unbounded-length expression is ever fed into the parser, one can prevent the parser from constructing a pathologically large AST and avoid potential memory exhaustion. In short, pre-validate and cap input size as a safeguard in the absence of the patch.

Impact

For European organizations, the primary impact of CVE-2025-29786 is the risk of denial-of-service (DoS) conditions in applications using vulnerable versions of the expr-lang library. Such DoS events can lead to service outages, degraded performance, and potential disruption of critical business processes, especially in sectors relying on Go-based microservices, automation, or configuration evaluation that utilize expr. Memory exhaustion could also affect containerized environments or cloud-native deployments common in Europe, potentially causing cascading failures or increased operational costs. Since the vulnerability does not compromise confidentiality or integrity, the impact is limited to availability. However, availability disruptions in critical infrastructure, financial services, or public sector applications could have significant operational and reputational consequences. The absence of authentication or user interaction requirements means that any exposed service accepting expressions could be targeted remotely, increasing the attack surface. Organizations with strict uptime requirements or those operating in regulated industries must prioritize mitigation to maintain compliance and service reliability.

Summary

CVE-2025-29786 affects the expr-lang expression evaluation library for the Go programming language, specifically versions before 1.17.0. The vulnerability arises from the lack of resource allocation limits during parsing of input expressions. When the parser receives an unboundedly large input string, it attempts to compile the entire expression, generating an Abstract Syntax Tree (AST) node for each component. This process can consume excessive memory, leading to an Out-Of-Memory (OOM) crash of the hosting process. The root cause is the absence of throttling or limits on the number of AST nodes or memory usage during compilation. This vulnerability is categorized under CWE-770: Allocation of Resources Without Limits or Throttling. The issue is particularly relevant in scenarios where input size is not constrained or validated, such as exposed APIs or services accepting user-supplied expressions. The vulnerability has been addressed in expr version 1.17.0 by introducing compile-time safeguards that limit AST node count and memory consumption, aborting compilation safely if limits are exceeded. For users unable to upgrade immediately, the recommended mitigation is to enforce strict input size restrictions before parsing, such as maximum character counts or node limits, to prevent resource exhaustion. The CVSS v3.1 base score is 7.5 (high), reflecting the vulnerability's potential to cause denial-of-service without requiring authentication or user interaction. No known exploits have been reported in the wild as of the publication date.

CWE-770Allocation of Resources Without Limits or Throttling (opens in a new tab)
Base weaknessLikelihood of exploit: HighCWE Top 25 (2025): #25
The product allocates a reusable resource or group of resources on behalf of an actor without imposing any intended restrictions on the size or number of resources that can be allocated.
Requirements
Clearly specify the minimum and maximum expectations for capabilities, and dictate which behaviors are acceptable when resource allocation reaches limits.
Architecture and Design
Limit the amount of resources that are accessible to unprivileged users. Set per-user limits for resources. Allow the system administrator to define these limits. Be careful to avoid CWE-410.
Architecture and Design
Design throttling mechanisms into the system architecture. The best protection is to limit the amount of resources that an unauthorized user can cause to be expended.
OWASP Cheat Sheets
Abuse Case (opens in a new tab)
OWASP ASVS 4.0.3
V8.1.4 (opens in a new tab)
V13.4.1 (opens in a new tab)
V11.1.4 (opens in a new tab)
Attack patterns
XML Ping of the Death (opens in a new tab)
Exponential Data Expansion (opens in a new tab)
Serialized Data Parameter Blowup (opens in a new tab)
Serialized Data with Nested Payloads (opens in a new tab)
Oversized Serialized Data Payloads (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 23 Jan 2026, 17:05 UTC

WeaknessesCWE-770

Technical details

References

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