Bug 2491401 (CVE-2026-53550)

Summary:	CVE-2026-53550 js-yaml: js-yaml: Denial of Service via crafted YAML merge keys
Product:	[Other] Security Response	Reporter:	OSIDB Bzimport <bzimport>
Component:	vulnerability	Assignee:	Product Security <prodsec-ir-bot>
Status:	NEW ---	QA Contact:
Severity:	medium	Docs Contact:
Priority:	medium
Version:	unspecified	CC:	aadhikar, aazores, abarbaro, abrianik, abuckta, adudiak, akostadi, alizardo, amasferr, amctagga, anjoseph, anpicker, anthomas, anujha, aoconnor, aschwart, asoldano, aszczucz, ataylor, bbaranow, bbrownin, bdettelb, bmaxwell, bniver, boliveir, bparees, brasmith, bsmejkal, bstansbe, cdrage, chfoley, cmah, cochase, dbosanac, dbruscin, dfreiber, dkeler, dkuc, dlofthou, dmayorov, doconnor, dranck, drichtar, drow, dschmidt, dymurray, eaguilar, ebaron, eborisov, ehelms, ehugonne, erezende, ewittman, fdeutsch, flucifre, fmariani, ggainey, ggrzybek, gmalinko, gmeno, gparvin, groman, hasun, ibolton, istudens, ivassile, iweiss, jachapma, janstey, jburrell, jchui, jfula, jhe, jkoehler, jlanda, jlledo, jmatthew, jmontleo, jolong, jowilson, jpasqual, jprabhak, jraez, jreimann, juwatts, jwong, jwon, kaycoth, kshier, ktsao, kvanderr, lball, lchilton, lphiri, manissin, mbarnett, mbenjamin, mcarlett, mdessi, mhackett, mhulan, mosmerov, mposolda, mreynolds, mrizzi, mstipich, msvehla, nboldt, ngough, nipatil, nmoumoul, nwallace, nyancey, oaljalju, omaciel, ometelka, orabin, oramraz, osousa, pahickey, pantinor, parichar, pberan, pcattana, pcreech, pdelbell, pesilva, pgaikwad, pjindal, pmackay, progier, psrna, ptisnovs, rchan, rexwhite, rgodfrey, rhaigner, rhel-process-autobot, rjohnson, rkubis, rmartinc, rstancel, rstepani, rushinde, sdawley, sfeifer, simaishi, slucidi, smallamp, smullick, snegrini, sostapov, spichugi, sseago, ssilvert, stcannon, sthirugn, sthorger, stirabos, suppawar, swoodman, syedriko, tasato, tbordaz, tcunning, teagle, thason, thjenkin, tmalecek, tsedmik, ttakamiy, vashirov, vdosoudi, vereddy, veshanka, vkumar, vmuzikar, watson-tool-maintainers, wtam, xdharmai, yfang, yguenane
Target Milestone:	---	Keywords:	Security
Target Release:	---
Hardware:	All
OS:	Linux
Whiteboard:
Fixed In Version:		Doc Type:	---
Doc Text:	A flaw was found in js-yaml, a JavaScript YAML parser and dumper. A remote attacker can exploit this vulnerability by providing a specially crafted YAML document that repeatedly uses the same alias in a merge sequence. This can lead to algorithmic CPU exhaustion, causing the Node.js worker or event loop to be blocked for an extended period, resulting in a denial of service (DoS) for the affected system.	Story Points:	---
Clone Of:		Environment:
Last Closed:		Type:	---
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:

Description OSIDB Bzimport 2026-06-22 16:01:24 UTC

js-yaml is a JavaScript YAML parser and dumper. Prior to 4.2.0, a crafted YAML document can trigger algorithmic CPU exhaustion in js-yaml merge-key processing (<<) by repeating the same alias many times in a merge sequence. This causes quadratic parse-time behavior relative to input size and can block a Node.js worker/event loop for seconds with a relatively small payload (tens of KB), resulting in denial of service. The issue is in merge handling inside lib/loader.js. This vulnerability is fixed in 4.2.0.