CVE-2026-41637
CVE-2026-41637 is a low-severity vulnerability in Nlnetlabs Unbound with a CVSS 3.x base score of 3.7. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-772.
Key facts
- Severity: Low (CVSS 3.x base score 3.7)
- EPSS exploit prediction: 0% (19th percentile)
- Actively exploited: Not listed in CISA KEV
- Weakness: CWE-772
- Affected product: Nlnetlabs Unbound
- Published:
- Last modified:
Description
In NLnet Labs Unbound 1.22.0 up to and including 1.25.1, client terminated DNS-over-QUIC (DoQ) queries are not accounted properly by Unbound resulting in low-cost inflation of the waiting number of replies for already in-flight resolution queries. This results in degradation of resolution service for new clients for already in-flight queries. A malicious actor can exploit the vulnerability by issuing DoQ queries for query names that need resolution and proceeding on immediately terminating the query by one of STOP_SENDING/RESET_STREAM/CONNECTION_CLOSE QUIC frames. Those terminated DoQ queries are not properly counted for and keep inflating the number of waiting replies for in-flight queries. When the maximum is reached, it results in silent query drops for new clients needing resolution for already in-flight queries. This vulnerability needs Unbound to be compiled with DoQ support ('--with-libngtcp2') and the 'quic-port' to be configured for the listening interfaces. Additionally, a malicious actor needs access to multiple source IPs to bypass the by-default configured 'wait-limit' option.
Frequently asked questions
- What is CVE-2026-41637?
- In NLnet Labs Unbound 1.22.0 up to and including 1.25.1, client terminated DNS-over-QUIC (DoQ) queries are not accounted properly by Unbound resulting in low-cost inflation of the waiting number of replies for already in-flight resolution queries. This results in degradation of resolution service for new clients for already in-flight queries. A malicious actor can exploit the vulnerability by issuing DoQ queries for query names that need resolution and proceeding on immediately terminating the query by one of STOP_SENDING/RESET_STREAM/CONNECTION_CLOSE QUIC frames. Those terminated DoQ queries are not properly counted for and keep inflating the number of waiting replies for in-flight queries. When the maximum is reached, it results in silent query drops for new clients needing resolution for already in-flight queries. This vulnerability needs Unbound to be compiled with DoQ support ('--with-libngtcp2') and the 'quic-port' to be configured for the listening interfaces. Additionally, a malicious actor needs access to multiple source IPs to bypass the by-default configured 'wait-limit' option.
- How severe is CVE-2026-41637?
- CVE-2026-41637 has a CVSS 3.x base score of 3.7, rated low severity. It is exploitable over network with high attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability low.
- Is CVE-2026-41637 being actively exploited?
- It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (19th percentile), an estimate of the probability of exploitation in the next 30 days.
- What products are affected by CVE-2026-41637?
- CVE-2026-41637 affects Nlnetlabs Unbound. See the affected-products list for the exact vulnerable versions.
- How do I fix CVE-2026-41637?
- Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
- When was CVE-2026-41637 published?
- CVE-2026-41637 was published on 2026-07-22 and last updated on 2026-07-24.
References
Affected products (1)
- cpe:2.3:a:nlnetlabs:unbound:*:*:*:*:*:*:*:*
More vulnerabilities in Nlnetlabs Unbound
- CVE-2026-42960 — Critical (CVSS 10.0): NLnet Labs Unbound up to and including version 1.25.0 is vulnerable to poisoning via promiscuous records for the…
- CVE-2026-33278 — Critical (CVSS 9.8): NLnet Labs Unbound 1.19.1 up to and including version 1.25.0 has a vulnerability in the DNSSEC validator that enables…
- CVE-2019-25042 — Critical (CVSS 9.8): Unbound before 1.9.5 allows an out-of-bounds write via a compressed name in rdata_copy. NOTE: The vendor disputes that…
- CVE-2019-25039 — Critical (CVSS 9.8): Unbound before 1.9.5 allows an integer overflow in a size calculation in respip/respip.c. NOTE: The vendor disputes…
- CVE-2019-25038 — Critical (CVSS 9.8): Unbound before 1.9.5 allows an integer overflow in a size calculation in dnscrypt/dnscrypt.c. NOTE: The vendor disputes…
- CVE-2019-25035 — Critical (CVSS 9.8): Unbound before 1.9.5 allows an out-of-bounds write in sldns_bget_token_par. NOTE: The vendor disputes that this is a…
All CVEs affecting Nlnetlabs Unbound →
Other CWE-772 vulnerabilities
- CVE-2020-12134 — Critical (CVSS 9.8): Nanometrics Centaur through 4.3.23 and TitanSMA through 4.2.20 mishandle access control for the syslog log.
- CVE-2017-15032 — Critical (CVSS 9.8): ImageMagick version 7.0.7-2 contains a memory leak in ReadYCBCRImage in coders/ycbcr.c.
- CVE-2017-14138 — Critical (CVSS 9.8): ImageMagick 7.0.6-5 has a memory leak vulnerability in ReadWEBPImage in coders/webp.c because memory is not freed in…
- CVE-2017-11641 — Critical (CVSS 9.8): GraphicsMagick 1.3.26 has a Memory Leak in the PersistCache function in magick/pixel_cache.c during writing of Magick…
- CVE-2020-14339 — High (CVSS 8.8): A flaw was found in libvirt, where it leaked a file descriptor for `/dev/mapper/control` into the QEMU process. This…
- CVE-2018-19760 — High (CVSS 8.8): cfg_init in confuse.c in libConfuse 3.2.2 has a memory leak.