CVE-2023-51258: Local memory leak in YASM preprocessor new_Token (1.3.0)

A small, targeted memory leak in the YASM assembler has emerged as a quietly dangerous availability problem: CVE-2023-51258 identifies a leak in the new_Token routine of the NASM preprocessor module that can be triggered by local users and, when exploited repeatedly, can exhaust memory and deny service to processes or hosts that run the affected YASM binaries.

Background​

YASM is a widely used, open-source x86/x86-64 assembler and a drop-in alternative to NASM for many build systems, compilers, and developer toolchains. The project’s 1.3.0 release is the version identified in this advisory. The vulnerability entry for CVE-2023-51258 describes a memory leak in the function new_Token inside the NASM preprocessor implementation (modules/preprocs/nasm/nasm-pp at line 1512 in the affected upstream source).
Distribution and vulnerability trackers (Ubuntu, Debian, SUSE, NVD and others) have cataloged the issue with a consistent description: a memory leak that allows a local attacker to produce a denial-of-service condition by consuming memory in the process running YASM. The commonly quoted CVSS v3 score is 5.5 (Medium), with vector AV:L/AC:L/PR:L/UI:N and an availability impact rated high because the flaw does not affect confidentiality or integrity but can disrupt service availability.

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What the vulnerability actually is — a technical breakdown​

Where the bug lives​

• The defect is reported in the NASM preprocessor module of YASM; the vulnerable routine is named new_Token. Audit records and vulnerability trackers point to the source file nasm-pp (the preprocessor) and identify the offending line range around 1512 in the upstream release referenced by the CVE.

What a memory leak means here​

A memory leak occurs when dynamically allocated memory is not released after it is no longer needed. In the context of a CLI assembler like YASM, a leak in token-handling code means that certain inputs — notably those that exercise preprocessor token creation paths — will consume more memory each time the code path runs. If an attacker can drive that behavior repeatedly (or cause many processes to execute the path concurrently), the host’s memory can be exhausted, processes can be terminated by the operating system’s OOM (out-of-memory) killer, or services that rely on YASM in build or CI tasks can be made unavailable. The recorded CWE classification is consistent with this: CWE‑401 (Missing Release of Memory After Effective Lifetime).

How the new_Token function becomes a vector​

The preprocessor’s tokenizer is the natural place to parse assembler directives, macros, and expressions. If token creation allocates structures that are not paired with the correct free paths — for example, on certain error exits, unexpected macro constructs, or specific preprocessor directives — memory will leak. The CVE identifies the precise function (new_Token), which indicates the leak is not a broad allocator bug but a localized resource-management error in the token lifecycle. That localization has two operational consequences:

• it limits the complexity of an exploit (the attacker only needs to craft input that exercises the token path), and
• it also suggests the fix can be small and surgical if maintainers add the missing frees or fix control flow paths that skip cleanup.

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Exploitability and real-world risk​

Local-only, but practical​

CVE-2023-51258 is a local vulnerability: an attacker must have the ability to run YASM (or cause YASM execution) on the target system. That means arbitrary remote exploitation is not indicated — this is not a remote network service bug — but it is very much an operational risk for build hosts, developer VMs, continuous integration systems, and restricted shells where untrusted users may run assembler tasks. Many vulnerability trackers reflect this reality by assigning the Local attack vector and a Medium base score.

Denial-of-service that accumulates​

A crucial property of memory-leak DoS issues is accumulation: each successful trigger may leak a small amount of memory, and repeated invocation will eventually exhaust resources. On shared build infrastructure that compiles many pieces or runs multiple assembler jobs, an attacker with low privileges can repeatedly call YASM with crafted inputs to force resource exhaustion. Distribution and scanner guidance explicitly warns of availability impact.

Proof-of-concept availability​

Several public vulnerability trackers and crash repositories reference example crash artifacts or test cases associated with the defect, and at least one public repository that collects crash inputs has a YASM folder with a readme entry for this case. Public exploit artifacts reduce the bar for lateral attackers and for automated scanning tools to detect vulnerable installations. Because the vulnerability is local and relatively straightforward to reproduce, the presence of PoC material increases the practical risk on multi-user or CI systems where attackers already have execution privileges. (github.com)
Caveat: not every publicly referenced crash sample is a fully weaponized exploit; many are minimal test cases that demonstrate a crash or leak. Still, they materially aid defenders and attackers alike by providing a clear path to trigger the issue.

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Which systems are affected​

• Upstream: YASM v1.3.0 is explicitly referenced by the CVE as the upstream release containing the defect. The YASM upstream project and its Git tags confirm the 1.3.0 release exists and is the version named against the issue.
• Linux distributions: major trackers have recorded affected package states. Debian’s security tracker shows the vulnerability tagged against the yasm source package across Debian suites, and Ubuntu’s advisory page lists the same description and the Medium CVSS rating while explaining why the distro may classify the priority as lower for its users. SUSE’s advisory lists the issue and provides its own assessment and handling decision (including distribution-specific severity and action notes). These entries show that the vulnerability was recognized across multiple packaging ecosystems and that remediation decisions varied by distribution.
• Microsoft/Azure distributions: scanning plugins and distribution advisories (for example, Azure Linux checks) also report the presence of the vulnerable package and provide local check guidance for detecting outdated YASM installations — a reminder that cloud-supplied or vendor-maintained Linux images may include vulnerable versions. Security scanners such as Nessus/Tenable call out missing updates for images that include the vulnerable YASM package.

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Vendor and distribution responses​

Responses have varied by vendor and distribution:

• Ubuntu and Debian: track the issue in their security databases and assign a CVSS of 5.5 with availability impact highlighted; Debian’s tracker shows the package tagged as vulnerable in several suites and tracks bug numbers for follow-up. Ubuntu’s page also rates operational priority (for Ubuntu’s specific environment) and links to upstream references.
• SUSE: included a vulnerability page that marks the issue and provides distribution-specific evaluation (in some cases, decisions like “won’t fix” for certain product lines where the risk or exposure is determined to be low). SUSE’s internal severity mapping can differ from NVD’s score because of how the package is used within SUSE-managed products.
• Upstream (YASM maintainers): the GitHub repository contains active issue tracking and release metadata; upstream fixes for similar issues have historically been small patches to preprocessor/tokenizer cleanup paths. Projects that embed YASM in their toolchains or ship it in images should monitor the upstream repository and distribution advisories.

Important note: distribution decisions (patch vs. “no DSA” or “won’t fix”) often depend on packaging policies, the expected trust model for CLI tools, and whether the package is included in the particular product image. That means operators must not assume that a distro’s “low priority” decision implies no action is needed — context matters.

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Mitigation guidance for system administrators and developers​

If you operate systems where YASM runs — CI runners, build servers, developer workstations, or developer containers — apply a layered approach: immediate operational mitigations, followed by a long-term patching plan.
Immediate mitigations (short-term, low-effort)

• Identify and inventory systems that include YASM. Use package managers (dpkg, rpm) or container image scans to list installations and versions of yasm. Prioritize build hosts and multi-tenant CI runners.
• Restrict who can execute YASM. Enforce least-privilege: limit execution to trusted build users and isolate build tasks with per-job user accounts or ephemeral containers so that a local, unprivileged user cannot repeatedly trigger assembler runs at scale.
• Monitor memory and job behavior. On CI hosts, add telemetry or alerts for unusual memory growth in assembler or build processes (watch for repeated invocations leaking memory).
• Use resource controls. Apply cgroups, ulimits, or container memory limits to prevent a single process from consuming host memory and causing system-wide outages.

Patching and longer-term fixes

• Apply an upstream or distribution patch when available. Watch Debian/Ubuntu/SUSE advisories and the YASM upstream repository for a targeted fix that adds the missing free calls or corrects the token lifecycle.
• Rebuild images and CI runners after the fix is applied. For cloud or image-based deployments, replace running images with patched versions rather than in-place edits where possible.
• For custom builds, backport the small fix into your internal package (if you must run an older YASM release), but do so with careful testing and code review — resource management fixes must be validated under stress to ensure there are no regressions.

Developer and packager guidance

• If you package YASM for distribution, include regression tests that exercise the preprocessor token paths; add leak-detection runs to CI where feasible.
• If you embed YASM into developer tooling or images, ensure the build and runtime environments are considered: whether the assembler runs on behalf of untrusted inputs and whether the process should be sandboxed.

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Operational impact and threat model​

• High-impact scenarios include shared CI infrastructure and multi-user developer servers where untrusted users can run assembler processes. An attacker who can repeatedly invoke the vulnerable token path may cause job failures, resource exhaustion, and interruption of build pipelines — a real availability problem for development organizations.
• Lower-impact scenarios are single-user developer desktops or tightly constrained build hosts where only trusted build agents run YASM; here, the practical risk is smaller but not zero, because untrusted input may still arrive from source trees or third-party components.
• The vulnerability is not a confidentiality or integrity issue, and there is no public indication of remote code execution arising from the reported memory leak alone. Nonetheless, availability attacks against build infrastructure can have cascading operational consequences (failed releases, delayed CI, and resource churn). Multiple trackers and distribution advisories emphasize that availability impact, even if the bug itself is narrow.

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Why this matters to WindowsForum readers​

Many Windows-focused toolchains and cross-compilers rely on Linux-compiled assembler tools or include YASM binaries in crDevelopment teams that produce multi-platform artifacts, maintain CI pipelines, or ship container images used by heterogeneous developer teams should treat local DoS defects seriously: a single vulnerable package in a shared build image can become a persistent source of disruption. Community discussion and crash-collection repositories have already cataloged test cases that make detection straightforward for both defenders and attackers, so patching or applying the mitigations above should be prioritized for shared infrastructure. (github.com)
(Community visibility: technical threads and aggregated vulnerability trackers in open-source forums have discussed YASM issues in multiple contexts — for example, pages that index project vulnerabilities and crash examples — underscoring how simple crash artifacts circulate among practitioners and escalate operational concern. )

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Recommendations — a practical checklist​

• Inventory: Find any yasm binaries or packages in images, containers, and hosts. Prioritize CI, build servers, and VM images.
• Isolate and limit: Apply resource limits and restrict which accounts can execute YASM; run untrusted builds in isolated containers with memory limits.
• Patch: Monitor upstream YASM and your distribution’s trackers and apply fixes as soon as a patched package or upstream commit is available. If no patch exists in your distro, consider rebuilding from upstream source with the fix.
• Test: Run regression and memory-leak detection (ASAN/valgrind where applicable) on build hosts after upgrades to ensure no regressions and that the leak is resolved.
• Monitor: Add alerts for abnormal memory growth and failed builds that might indicate attempted exploitation.
• Document: Record affected hosts and remediation steps in your change control and incident playbooks so you can demonstrate closure during audits.

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Strengths of the response landscape — and remaining risks​

What’s good:

• The vulnerability is well-scoped and documented across multiple trusted trackers (NVD, Debian/Ubuntu security trackers), which makes detection and inventory straightforward.
• The fix, when implemented, is likely to be compact and localized to token lifecycle code paths; that reduces the risk of long, invasive refactors and makes backporting feasible for distribution maintainers.

What’s still risky:

• Not all distributions or vendor-maintained images will treat the CLI tool the same way; “won’t fix” or low-priority classifications in product catalogs can leave some images unpatched even after upstream fixes are available. Operators must verify their own images rather than relying on blanket distribution statements.
• Public PoC/test cases exist in crash-collection repositories; that lowers the bar for attackers in multi-user environments. Even if exploitation requires local access, shared CI and containerized development environments commonly provide the local execution rights that turn a low-complexity vulnerability into an operational headache. (github.com)
• Because memory leaks can be subtle (small per-invocation), they can evade detection until repeated or concurrent exploitation produces catastrophic OOM behavior — a reason to apply proactive resource controls and to include leak checks in CI for critical toolchains.

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Final analysis​

CVE-2023-51258 is an example of how a small, seemingly trivial resource-management bug in a developer tool can translate into a tangible operational risk. The vulnerability is not a remote code execution worm; it is a local, denial-of-service vector that becomes important in shared and automated environments. The community and major distribution trackers have cataloged the flaw and assigned a Medium CVSS base score emphasizing availability risk; public crash artifacts exist and make detection and triggering straightforward where execution privileges exist.
For administrators and build engineers: assume your CI runners, build images, and developer VMs are valuable assets to protect. Inventory YASM, apply available patches or rebuild with upstream fixes, isolate untrusted workloads, and add memory and resource limits to stop a local leak from becoming a system-wide outage. For packagers and upstream developers: prioritize a small, well-tested fix to the token lifecycle and add regression tests that exercise preprocessor code paths under memory-stress conditions. That combination — surgical code repair, distribution coordination, and operational hardening — is the most reliable path to neutralizing this class of vulnerability before it causes production outages.

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Conclusion: CVE-2023-51258 is a focused but real availability risk for environments that run YASM 1.3.0 in multi-tenant, CI, or cloud-image contexts. The technical fix is likely straightforward, but the operational remediation requires careful inventory, timely patching, and pragmatic resource controls to prevent local exploitation from turning into disruptive downtime.

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Source: MSRC Security Update Guide - Microsoft Security Response Center